Links marked See on Amazon are affiliate links — buy through one and we earn a commission at no cost to you. How that works, and how the picks are made.
For most reef sumps, a Reef Octopus Classic one size over what the box says for your tank — the 150-INT for a 75, not the 110 — because the box's "medium" is the air rule's "light". For 120 gallons and up, or a tank you mean to stock hard, the Regal: the same body with a controllable pump. In a tight sump, a Nyos Quantum, the one maker whose heavy rating is under what its air supports. On a budget, a Bubble Magus Curve bought by the air column, not the box — the Curve 7 is a 46 gallon skimmer at heavy stocking, sold as a 90. And whichever you buy, size it for the water you have: a "75 gallon" reef with sand, rock and a sump is 85 gallons to the skimmer.
A skimmer's box prints a tank size in gallons, sometimes three of them — light, medium, heavy — and none of the three is a measurement. The measurement is the air draw: liters of air per hour the pump pulls through the water, which is the bubble surface the organics stick to. The hobby's sizing rule ties the two together — about 1 L/h of air per liter of system water for a lightly stocked tank, 1.5× that for a normal reef, 3× for fish and SPS — and two makers publish ratios that say the same thing. Every figure on this page is that rule run on each skimmer's own air figure and on the water a reef actually holds, from the true water volume calculator's engine: a standard display filled to the overflow, 1.5 in of sand, 0.75 lb of rock per labeled gallon, and a sump holding 25 % of the display. Your own tank goes through the calculator.
Which protein skimmer for your tank
For each standard display set up as a reef, the water the skimmer sees, the air that water needs at medium and heavy stocking, and the smallest skimmer here whose air covers it with 15 % in hand. "Best value" ranges over every model; "best overall" only over the lines with a maker behind the pump and a spares network. The last column is the smallest skimmer that covers the tank at heavy stocking — fish and SPS — from any line.
| Display | Water the skimmer sees | Air needed medium · heavy | Best value, medium | Best overall, medium | Heavy stocking |
|---|---|---|---|---|---|
| 40 gallon breeder | 178 L · 47 gal | 267 · 535 L/h | Simplicity 120DC 360 L/h · 1.35× the need | Reef Octopus Classic 110-INT 420 L/h · 1.57× the need | Simplicity 240DC 660 L/h · 1.23× the need |
| 55 gallon | 231 L · 61 gal | 346 · 693 L/h | Reef Octopus Classic 110-INT 420 L/h · 1.21× the need | Reef Octopus Classic 110-INT 420 L/h · 1.21× the need | Reef Octopus Regal 150-INT 900 L/h · 1.3× the need |
| 75 gallon | 320 L · 85 gal | 480 · 960 L/h | Simplicity 240DC 660 L/h · 1.38× the need | Reef Octopus Classic 150-INT 720 L/h · 1.5× the need | — needs 1,104 L/h; the biggest here pulls 1,500 |
| 90 gallon | 369 L · 97 gal | 553 · 1,106 L/h | Simplicity 240DC 660 L/h · 1.19× the need | Reef Octopus Classic 150-INT 720 L/h · 1.3× the need | Reef Octopus Regal 200-INT 1,500 L/h · 1.36× the need |
| 120 gallon | 492 L · 130 gal | 738 · 1,475 L/h | Reef Octopus Regal 150-INT 900 L/h · 1.22× the need | Reef Octopus Regal 150-INT 900 L/h · 1.22× the need | — needs 1,697 L/h; the biggest here pulls 1,500 |
| 150 gallon | 655 L · 173 gal | 983 · 1,966 L/h | Reef Octopus Regal 200-INT 1,500 L/h · 1.53× the need | Reef Octopus Regal 200-INT 1,500 L/h · 1.53× the need | — needs 2,260 L/h; the biggest here pulls 1,500 |
| 180 gallon | 773 L · 204 gal | 1,160 · 2,319 L/h | Reef Octopus Regal 200-INT 1,500 L/h · 1.29× the need | Reef Octopus Regal 200-INT 1,500 L/h · 1.29× the need | — needs 2,667 L/h; the biggest here pulls 1,500 |
| 210 gallon | 906 L · 239 gal | 1,359 · 2,718 L/h | — needs 1,563 L/h; the biggest here pulls 1,500 | — needs 1,563 L/h; the biggest here pulls 1,500 | — needs 3,126 L/h; the biggest here pulls 1,500 |
Standard displays filled to the overflow, minus 1.5 in of aragonite and 0.75 lb of rock per labeled gallon, plus a sump at 25 %; air at 1.5 and 3 L/h per liter of that water; the pick is the smallest model whose air meets the need with 15 % to spare — a maker's air figure is a clean-wheel maximum — without being more than the tank can feed. All product links on this page are Amazon affiliate links. Your own rock, sand and sump go through the calculator.
At a glance
| Skimmer | Pump | Air | Box says | Air says, light | Water depth | Street price |
|---|---|---|---|---|---|---|
| Reef Octopus Classic (110-INT / 150-INT) | AC | 420–720 L/h | 130 / 210 gal | 111 / 190 gal | 6–8 in | $240–380 |
| Reef Octopus Regal (150-INT / 200-INT) | DC | 900–1,500 L/h | 210 / 400 gal | 238 / 396 gal | 7–8.5 in | $525–870 |
| Nyos Quantum (120 / 160) | AC | 500–1,500 L/h | 125 / 250 gal | 132 / 396 gal | 7.9–8.7 in | $400–530 |
| Red Sea Reefer Skimmer RSK-300 | AC | 500 L/h | 160 gal | 132 gal | 6.3–7.9 in | $380–420 |
| Simplicity DC (120DC / 240DC) | DC | 360–660 L/h | 120 / 240 gal | 95 / 174 gal | 6–8 in | $260–320 |
| Bubble Magus Curve (5 / 7) | AC | 300–520 L/h | 120 / 180 gal | 79 / 137 gal | 9.5–11 in | $190–365 |
| Tunze Comline DOC 9004 (AC / DC) | DC | 150–200 L/h | 65 / 79 gal | 40 / 53 gal | 8.9–9.7 in | $200–260 |
From each maker's page or a specialist retailer's listing, checked on the date at the top; where the two disagree the product card says so and the lower figure is used. "Box says" is the maker's headline gallons per model; "air says" is the system water the model's air supports lightly stocked. Prices are broad bands from specialist retailers, not Amazon.
How we ranked them
Three things, in this order. The air, against the box — a skimmer that pulls what its rating needs is honest, one that needs a multiplier is sold a size too big, and the chart below scores every model. What it is like to own — whether the sump depth it wants is a depth sumps run at; whether the pump is a stocked part or a house brand; BRS's depth measurements, where it tested a model; noise and tuning by the reef forums' consensus. Then the ordinary things: footprint, DC or AC, price. Every model here is sold on Amazon, so every product link is an affiliate link; the price bands are from the specialist retailers and commission is not a factor in the order.
The picks
Reef Octopus Classic (110-INT / 150-INT)
The sump under most reef tanks from 55 to 150 gallons: a plain AC pinwheel that pulls exactly the air it says, a body every retailer stocks parts for, and the best price per liter of air on the page.
- Pump
- Aquatrance pinwheel, AC
- Air
- 420–720 L/h
- Draw
- 9–18 W
- Footprint
- 10.4 × 7 in · 12.4 × 8.7 in
- Height
- 19.8 in · 22 in
- Water depth
- 6–8 in
- Warranty
- 1 year
- Street price
- $240–380 (2026-08)
| Size | Box says | The air supports (L / M / H) | Standard reefs it covers | Water depth · a year |
|---|---|---|---|---|
| Classic 110-INT · 9 W → | 420 L/h air · 130 / 90 / 60 gal | 111 / 74 / 37 gal | light 29–90 · medium 29–65 · heavy 29–37 · too much for 20 and under | 7–8 in of water · $14/yr |
| Classic 150-INT · 18 W → | 720 L/h air · 210 / 150 / 120 gal | 190 / 127 / 63 gal | light 40–150 · medium 40–125 · heavy 40–55 · too much for 37 and under | 6–8 in of water · $28/yr |
"Box says" is the maker's air draw and tank rating — light / medium / heavy where the maker prints them (source: Reef Octopus and distributor listings via Premium Aquatics); the size links go where the button below does. "The air supports" is the system water that air covers at 1, 1.5 and 3 L/h per liter. "Standard reefs" is the labeled sizes it covers at each stocking, on the reef setup above, and where it is more skimmer than the tank can feed. The year is at full draw, $0.18/kWh.
- The 150-INT pulls 720 L/h on 18 W — the best air per watt of any AC skimmer here — and BRS's depth test found it barely cares where the sump level sits within a 3 in band.
- Ratings the air supports for a light load (the 110-INT's 130 gal is 111 by the air rule), not the fantasy figures some boxes print.
- Parts, pumps and cups stocked everywhere; the pinwheel is a known quantity twenty years on.
- The 110-INT is depth-sensitive: BRS measured air dropping an inch either side of its 7–8 in window, so it wants a stand cut to size.
- AC: no turn-down, so the only tuning is the wedge pipe and the water level.
- The heavy-stocking ratings are the maker's optimism — a 75 gallon reef with fish and SPS is over a 110-INT.
Reef Octopus Regal (150-INT / 200-INT)
A 120 to 250 gallon reef stocked the way people actually stock them — fish and SPS — where the air a Classic pulls is not enough and a controllable pump lets you match the skimmer to the load.
- Pump
- VarioS-S controllable pinwheel, 24 V DC
- Air
- 900–1,500 L/h
- Draw
- 25–40 W
- Footprint
- 11.4 × 7.5 in · 14.6 × 9.8 in
- Height
- 22.6 in · 23.4 in
- Water depth
- 7–8.5 in
- Warranty
- 1 year
- Street price
- $525–870 (2026-08)
| Size | Box says | The air supports (L / M / H) | Standard reefs it covers | Water depth · a year |
|---|---|---|---|---|
| Regal 150-INT · 25 W → | 900 L/h air · up to 210 gal | 238 / 159 / 79 gal | light 55–180 · medium 55–125 · heavy 55–65 · too much for 40 and under | 7–8.5 in of water · $39/yr |
| Regal 200-INT · 40 W → | 1,500 L/h air · up to 400 gal | 396 / 264 / 132 gal | light 90–210 · medium 90–210 · heavy 90–125 · too much for 75 and under | 7–8.5 in of water · $63/yr |
"Box says" is the maker's air draw and tank rating — light / medium / heavy where the maker prints them (source: Reef Octopus and retailer listings via SaltwaterAquarium.com and Bulk Reef Supply); the size links go where the button below does. "The air supports" is the system water that air covers at 1, 1.5 and 3 L/h per liter. "Standard reefs" is the labeled sizes it covers at each stocking, on the reef setup above, and where it is more skimmer than the tank can feed. The year is at full draw, $0.18/kWh.
- 900 L/h from the 150-INT and 1,500 from the 200-INT, controllable: the one honest way to buy a skimmer for the tank you will have in two years and run it for the tank you have now.
- The Regal 150-INT's box rating of 210 gal is under what its air supports lightly stocked — a rare conservative figure.
- Same 6 in / 8 in hybrid-cone bodies as the Classics, so the tuning behavior and the spares are known.
- Twice the price of the Classic for the same body and a controller; you are paying for the pump.
- Reef Octopus prints no light/medium/heavy breakdown for the Regals — the "up to 210" is a light-load number.
- Three parts to fail — pump, controller, power supply — like every DC skimmer, and a one-year warranty.
Nyos Quantum (120 / 160)
A cramped sump: the Quantum 120 pulls more air than a Classic 110 from a 6 × 8 in footprint, and the 160 pulls a Regal 200's air on 18 W. The ratings on the box are the most conservative on this page.
- Pump
- Quantum hybrid wheel, AC
- Air
- 500–1,500 L/h
- Draw
- 8–18 W
- Footprint
- 5.9 × 8.3 in · 7.1 × 9.8 in
- Height
- 18.3 in · 20.9 in
- Water depth
- 7.9–8.7 in
- Warranty
- 2 years
- Street price
- $400–530 (2026-08)
| Size | Box says | The air supports (L / M / H) | Standard reefs it covers | Water depth · a year |
|---|---|---|---|---|
| Quantum 120 · 8 W → | 500 L/h air · 125 / 75 / 50 gal | 132 / 88 / 44 gal | light 29–125 · medium 29–75 · heavy 29–37 · too much for 20 and under | 7.9–8.7 in of water · $13/yr |
| Quantum 160 · 18 W → | 1,500 L/h air · 250 / 150 / 75 gal | 396 / 264 / 132 gal | light 90–210 · medium 90–210 · heavy 90–125 · too much for 75 and under | 7.9–8.7 in of water · $28/yr |
"Box says" is the maker's air draw and tank rating — light / medium / heavy where the maker prints them (source: Nyos product pages and Bulk Reef Supply listings); the size links go where the button below does. "The air supports" is the system water that air covers at 1, 1.5 and 3 L/h per liter. "Standard reefs" is the labeled sizes it covers at each stocking, on the reef setup above, and where it is more skimmer than the tank can feed. The year is at full draw, $0.18/kWh.
- The Quantum 160's 1,500 L/h on 18 W is twice the air per watt of the next best skimmer here — if the figure holds on your bench, nothing touches it.
- Nyos rates heavy at 75 gal for the 160 where the air supports 132: the one maker whose "heavy" is safe to believe.
- Small footprints, a two-year warranty, and a bubble plate that makes tuning forgiving.
- The 1,500 L/h figure is the maker's "air max" on retailer spec sheets and is not on the Nyos page itself; treat it as a ceiling. The card's ranges use it.
- A narrow depth window — the manual says about 21 cm (8.3 in) of water, so most sumps want a stand or a baffle change.
- Dearest AC skimmer here per liter of air at the small end; the 120 is a $400 skimmer for a 75.
Red Sea Reefer Skimmer RSK-300
A 75 to 120 gallon mixed reef, and anyone who wants a rating they can read: Red Sea prints fish-only, mixed reef and SPS figures in a 3 : 2 : 1 ratio — the air rule's ratio exactly.
- Pump
- Sicce PSK-600 needle wheel, AC
- Air
- 500 L/h
- Draw
- 12 W
- Footprint
- 9.1 × 8.3 in
- Height
- 21 in
- Water depth
- 6.3–7.9 in
- Warranty
- 1 year
- Street price
- $380–420 (2026-08)
| Size | Box says | The air supports (L / M / H) | Standard reefs it covers | Water depth · a year |
|---|---|---|---|---|
| RSK-300 · 12 W → | 500 L/h air · 240 / 160 / 80 gal | 132 / 88 / 44 gal | light 29–125 · medium 29–75 · heavy 29–37 · too much for 20 and under | 6.3–7.9 in of water · $19/yr |
"Box says" is the maker's air draw and tank rating — light / medium / heavy where the maker prints them (source: Red Sea product table and Bulk Reef Supply listing); the size links go where the button below does. "The air supports" is the system water that air covers at 1, 1.5 and 3 L/h per liter. "Standard reefs" is the labeled sizes it covers at each stocking, on the reef setup above, and where it is more skimmer than the tank can feed. The year is at full draw, $0.18/kWh.
- The only maker here that defines its stocking levels by what is in the tank (fish only / mixed reef / SPS) and scales them 3 : 2 : 1 — 240 / 160 / 80 gal on 500 L/h.
- A Sicce pump, a 6–8 in window that suits the shallow chambers of the Reefer sumps, and a diffusion chamber that keeps the neck quiet.
- Fits the Reefer 250–350 sumps it was drawn for without a stand.
- The SPS figure (80 gal) is still a little over what 500 L/h supports at the heavy rule (66 gal); the fish-only figure is 1.8× the light rule.
- A single size: nothing for a nano and nothing over about 120 gallons stocked normally.
- AC, and the cup drain is an optional extra.
Simplicity DC (120DC / 240DC)
A controllable skimmer at an AC price: the 240DC pulls a Classic 150's air with a dial on it for $320, if you accept a house brand's support and the maker's more optimistic ratings.
- Pump
- Simplicity needle wheel, 24 V DC
- Air
- 360–660 L/h
- Draw
- 17–18 W
- Footprint
- 6.7 × 6.3 in · 8.3 × 7.9 in
- Height
- 18.7 in · 19.5 in
- Water depth
- 6–8 in
- Warranty
- 1 year
- Street price
- $260–320 (2026-08)
| Size | Box says | The air supports (L / M / H) | Standard reefs it covers | Water depth · a year |
|---|---|---|---|---|
| 120DC · 17 W → | 360 L/h air · 120 / 90 / 60 gal | 95 / 63 / 32 gal | light 29–75 · medium 29–55 · heavy a 29 · too much for 20 and under | 6–8 in of water · $27/yr |
| 240DC · 18 W → | 660 L/h air · 240 / 180 / 120 gal | 174 / 116 / 58 gal | light 40–150 · medium 40–90 · heavy a 40 · too much for 37 and under | 6–8 in of water · $28/yr |
"Box says" is the maker's air draw and tank rating — light / medium / heavy where the maker prints them (source: Simplicity Aquatics pages and Bulk Reef Supply listings); the size links go where the button below does. "The air supports" is the system water that air covers at 1, 1.5 and 3 L/h per liter. "Standard reefs" is the labeled sizes it covers at each stocking, on the reef setup above, and where it is more skimmer than the tank can feed. The year is at full draw, $0.18/kWh.
- The 240DC: 660 L/h controllable for the price of a Classic 150 — the cheapest controllable air on the page.
- Small footprints (the 120DC is 6.7 × 6.3 in) and a 6–8 in window that suits all-in-one and shallow sumps.
- Sold and supported by Bulk Reef Supply, which is where the parts are.
- The air figures disagree: the maker's site says 570 and 780 L/h, the BRS listings 360 and 660. We use the lower ones, and the ranges here are on those.
- The ratings are the optimistic kind: "240 gal light" on 660 L/h is 1.4× what the air rule allows, and "120 heavy" is 2×.
- A house-brand DC pump: fine while BRS stocks the pump, a paperweight if it stops.
Bubble Magus Curve (5 / 7)
A first sump on a budget, bought one size larger than the box suggests: the Curve 7 is a good 90 gallon skimmer sold as a 180.
- Pump
- SP needle wheel, AC
- Air
- 300–520 L/h
- Draw
- 8–16 W
- Footprint
- 7.3 × 7.1 in · 9.3 × 7.9 in
- Height
- 18.5 in · 20.8 in
- Water depth
- 9.5–11 in
- Warranty
- 1 year
- Street price
- $190–365 (2026-08)
| Size | Box says | The air supports (L / M / H) | Standard reefs it covers | Water depth · a year |
|---|---|---|---|---|
| Curve 5 · 8 W → | 300 L/h air · 120 / 90 / 55 gal | 79 / 53 / 26 gal | light 20–65 · medium 20–40 · heavy a 20 · too much for 15 and under | 9.5–11 in of water · $13/yr |
| Curve 7 · 16 W → | 520 L/h air · 180 / 125 / 90 gal | 137 / 92 / 46 gal | light 37–125 · medium 37–75 · heavy a 37 · too much for 29 and under | 9.5–11 in of water · $25/yr |
"Box says" is the maker's air draw and tank rating — light / medium / heavy where the maker prints them (source: Bulk Reef Supply listings and bubble-magus.net); the size links go where the button below does. "The air supports" is the system water that air covers at 1, 1.5 and 3 L/h per liter. "Standard reefs" is the labeled sizes it covers at each stocking, on the reef setup above, and where it is more skimmer than the tank can feed. The year is at full draw, $0.18/kWh.
- The cheapest branded skimmers with a real air figure: the Curve 5 is under $200.
- The wine-glass body tunes easily and the cup lifts off without tools.
- Ten years of the same design; pumps and cups are easy to find.
- The most optimistic ratings here: "180 gal light" on 520 L/h is 1.3× the air rule and "90 gal heavy" is 2×. Buy by the air column, not the box.
- Needs 9.5–11 in of water — deeper than most sumps run, and the one problem a stand cannot fix.
- The Curve 7's wattage is printed as 16 W by BRS and 28 W by the maker; the newer SP pumps draw more.
Tunze Comline DOC 9004 (AC / DC)
A nano or an all-in-one up to about 40 gallons, where nothing else fits: a magnet-mounted box that hangs in the back chamber or the sump and pulls 150–200 L/h on 4–10 W.
- Pump
- Foamer impeller, AC or DC
- Air
- 150–200 L/h
- Draw
- 4–10 W
- Footprint
- 4.3 × 3.5 in · 4.3 × 3.5 in
- Height
- 12 in · 12 in
- Water depth
- 8.9–9.7 in
- Warranty
- 2 years
- Street price
- $200–260 (2026-08)
| Size | Box says | The air supports (L / M / H) | Standard reefs it covers | Water depth · a year |
|---|---|---|---|---|
| 9004 · 4 W → | 150 L/h air · 60 / 40 / 20 gal | 40 / 26 / 13 gal | light 10–37 · medium 10–20 · heavy a 10 · too much for 5.5 and under | 8.9–9.7 in of water · $6.31/yr |
| 9004 DC · 10 W → | 200 L/h air · 60 / 40 / 20 gal | 53 / 35 / 18 gal | light 15–40 · medium 15–29 · heavy a 15 · too much for 10 and under | 8.9–9.7 in of water · $16/yr |
"Box says" is the maker's air draw and tank rating — light / medium / heavy where the maker prints them (source: Tunze product pages and Bulk Reef Supply listings); the size links go where the button below does. "The air supports" is the system water that air covers at 1, 1.5 and 3 L/h per liter. "Standard reefs" is the labeled sizes it covers at each stocking, on the reef setup above, and where it is more skimmer than the tank can feed. The year is at full draw, $0.18/kWh.
- A 4.3 × 3.5 in footprint that mounts on a magnet in a rear chamber — the reason it is on the page.
- Tunze publishes the honest scaling: use a skimmer on 60 % of its rating for a mixed reef, 40 % for SPS, 30 % for SPS with a heavy fish load.
- 4 W. The AC version costs $6 a year to run.
- 150–200 L/h is a 20–40 gallon skimmer at normal stocking; the "79 gal" on the DC box is a fish-light figure.
- A 9–10 in immersion depth is deeper than most all-in-one chambers; check before buying.
- It is a Comline, not a cone: a surface-skimming box with a foamer, quieter and less efficient per watt than a needle wheel.
The box rating against the air
Take the rule at its word and run it backwards: a skimmer's air figure, divided by 1, 1.5 and 3, is the system water it supports at light, medium and heavy stocking. Put that beside the box. The Reef Octopus Classic 110-INT pulls 420 L/h and is rated 130 / 90 / 60; the air says 111 / 74 / 37 gal — the light figure is honest (1.17× the rule) and the heavy figure is not. The Bubble Magus Curve 7 pulls 520 L/h and is rated 180 / 125 / 90; the air says 137 / 92 / 46 gal — the heavy rating is 2× what its air supports. The Nyos Quantum 160 runs the other way: rated 250 / 150 / 75 on 1,500 L/h, where the air supports 396 / 264 / 132 gal.
| Model | Air | Box: light / heavy | Air: light / heavy | Light rating is | Heavy rating is |
|---|---|---|---|---|---|
| Bubble Magus Curve 5 | 300 L/h | 120 / 55 gal | 79 / 26 gal | 1.51× the air | 2.08× the air |
| Simplicity 240DC | 660 L/h | 240 / 120 gal | 174 / 58 gal | 1.38× the air | 2.06× the air |
| Bubble Magus Curve 7 | 520 L/h | 180 / 90 gal | 137 / 46 gal | 1.31× the air | 1.97× the air |
| Simplicity 120DC | 360 L/h | 120 / 60 gal | 95 / 32 gal | 1.26× the air | 1.89× the air |
| Reef Octopus Classic 150-INT | 720 L/h | 210 / 120 gal | 190 / 63 gal | 1.1× the air | 1.89× the air |
| Red Sea RSK-300 | 500 L/h | 240 / 80 gal | 132 / 44 gal | 1.82× the air | 1.82× the air |
| Reef Octopus Classic 110-INT | 420 L/h | 130 / 60 gal | 111 / 37 gal | 1.17× the air | 1.62× the air |
| Tunze 9004 | 150 L/h | 60 / 20 gal | 40 / 13 gal | 1.51× the air | 1.51× the air |
| Nyos Quantum 120 | 500 L/h | 125 / 50 gal | 132 / 44 gal | 0.95× the air | 1.14× the air |
| Tunze 9004 DC | 200 L/h | 60 / 20 gal | 53 / 18 gal | 1.14× the air | 1.14× the air |
| Nyos Quantum 160 | 1,500 L/h | 250 / 75 gal | 396 / 132 gal | 0.63× the air | 0.57× the air |
Models whose makers publish a light and a heavy figure, most optimistic first. "× the air" is the box gallons divided by the gallons the model's air supports at that stocking; 1.00 is honest, under 1 is conservative. The Regals and the Simplicity 120DC's headline figures are on the chart.
Red Sea rates the RSK-300 at 240 gallons fish-only, 160 mixed reef and 80 SPS — a 3 : 2 : 1 scale, which is exactly what 1, 1.5 and 3 L/h per liter produce. Tunze says to use a skimmer on 60 % of its rating for a mixed reef, 40 % for SPS and 30 % for SPS with a heavy fish load. Neither maker uses the words "light, medium, heavy," and both say the same thing: the headline number is the fish-light number, and a normal reef needs the air of a skimmer rated half again over. The other makers print three gallon figures and leave you to guess which tank is "heavy"; the air column above is the guess removed.
The water a skimmer actually processes
The second number the box gets wrong is yours. A "75 gallon" reef is not 75 gallons of water to the skimmer: the display filled to the overflow holds 75, the sand bed and the rock take 9 back out, and the sump adds 19 — 85 gallons, 1.13× the label. Size on the display alone and you size for 66 and miss the 22 % of the water that is under the stand. The table runs the same setup across the standard sizes; the calculator runs it for your rock and your sump.
| Display | At the overflow | − sand and rock | + sump | Skimmed water | Air at medium |
|---|---|---|---|---|---|
| 40 gallon breeder | 42 gal | −5.5 gal | +11 gal | 47 gal · 178 L | 267 L/h |
| 55 gallon | 54 gal | −6.5 gal | +14 gal | 61 gal · 231 L | 346 L/h |
| 75 gallon | 75 gal | −9 gal | +19 gal | 85 gal · 320 L | 480 L/h |
| 90 gallon | 86 gal | −10 gal | +22 gal | 97 gal · 369 L | 553 L/h |
| 120 gallon | 115 gal | −13 gal | +29 gal | 130 gal · 492 L | 738 L/h |
| 150 gallon | 151 gal | −16 gal | +38 gal | 173 gal · 655 L | 983 L/h |
| 180 gallon | 180 gal | −20 gal | +45 gal | 204 gal · 773 L | 1,160 L/h |
| 210 gallon | 209 gal | −22 gal | +52 gal | 239 gal · 906 L | 1,359 L/h |
Display an inch below the rim (the overflow's level), 1.5 in of aragonite at 60 % solid, rock at 0.75 lb per labeled gallon and 1.2 kg per liter displaced, a sump running at 25 % of the display. The same engine as the calculator; a deep sand bed or a rock-heavy scape moves the middle column, a big sump the fourth.
The box says a Classic 110-INT is a 90 gallon skimmer at medium stocking, so it is the obvious buy for a 75. The 75's skimmed water is 320 L, which at 1.5 L/h per liter needs 480 L/h of air; the 110-INT pulls 420 — 88 % of the need. The 150-INT pulls 720, 1.5× the need, and covers the same tank stocked hard (960 L/h) only if you feed lightly. That is the whole page in one tank: the box is a lightly stocked number on a display-only volume, and both corrections point the same way.
Will it fit my sump?
Every body is designed for a band of water depth: below it the foam never climbs to the neck, above it the cup floods every time you feed. BRS measured the air draw an inch either side of the makers' windows and found some bodies (the Classic 150) indifferent across three inches and others (the Classic 110) losing air both ways. Sumps run at about 6 to 10 in; of the 13 models here, 8 fit an 8 in chamber as is, 3 fit 6 in and 2 fit 10 in. A sump that is too deep is fixed with a stand — the table says how tall. A sump that is too shallow is fixed only by raising the return chamber's baffle, which is a saw and a pane of glass, so the shallow cells are the ones to read before buying.
| Model | Body wants | Sump at 6 in | Sump at 8 in | Sump at 10 in |
|---|---|---|---|---|
| Tunze 9004 | 8.9–9.7 in | 2.9 in too shallow | 0.9 in too shallow | 0.3 in stand |
| Tunze 9004 DC | 8.9–9.7 in | 2.9 in too shallow | 0.9 in too shallow | 0.3 in stand |
| Bubble Magus Curve 5 | 9.5–11 in | 3.5 in too shallow | 1.5 in too shallow | fits |
| Simplicity 120DC | 6–8 in | fits | fits | 2 in stand |
| Reef Octopus Classic 110-INT | 7–8 in | 1 in too shallow | fits | 2 in stand |
| Nyos Quantum 120 | 7.9–8.7 in | 1.9 in too shallow | fits | 1.3 in stand |
| Red Sea RSK-300 | 6.3–7.9 in | 0.3 in too shallow | 0.1 in stand | 2.1 in stand |
| Bubble Magus Curve 7 | 9.5–11 in | 3.5 in too shallow | 1.5 in too shallow | fits |
| Simplicity 240DC | 6–8 in | fits | fits | 2 in stand |
| Reef Octopus Classic 150-INT | 6–8 in | fits | fits | 2 in stand |
| Reef Octopus Regal 150-INT | 7–8.5 in | 1 in too shallow | fits | 1.5 in stand |
| Reef Octopus Regal 200-INT | 7–8.5 in | 1 in too shallow | fits | 1.5 in stand |
| Nyos Quantum 160 | 7.9–8.7 in | 1.9 in too shallow | fits | 1.3 in stand |
The makers' windows from the product cards; "stand" is the height that brings a deeper sump into the window; "too shallow" is how far below the window the chamber runs. The Tunze mounts on a magnet and the figure is its immersion depth. Measure your chamber with the return pump running — the level with it off is the wrong number.
Read the 8 in column as the market: the Tunze 9004, Tunze 9004 DC, Bubble Magus Curve 5 and Bubble Magus Curve 7 want more water than a typical sump has, which is the one problem on this page a $15 stand cannot solve, and the reason the Curves are further down the list than their price would put them (the Tunze hangs on a magnet, so its figure is the depth its chamber must have). The Reef Octopus bodies and the Simplicity, at 6–8 in, sit in the shallow chambers of the all-in-one and Reefer sumps without a stand.
What each one costs to run
A skimmer runs 24 hours a day for as long as you own it, and the useful number is not the watts but the air per watt: how much bubble surface the pump buys with each watt. The table has every model. Two things stand out. The Nyos figures — 83 L/h per watt on the 160 and 63 on the 120 — are the maker's "air max" on a hybrid wheel; the 160's is 1.8× the next best pump here, the Reef Octopus Classic 110-INT at 47. Treat the Nyos numbers as ceilings until you have measured them, and know that even at two-thirds the 160 would still lead. And the year's cost is small everywhere: the dearest to run here is the Reef Octopus Regal 200-INT at $63 a year flat out, which is why the pump's efficiency matters for the air it gives you, not the bill.
| Model | Air | Draw | Air per watt | A year |
|---|---|---|---|---|
| Nyos Quantum 160 | 1,500 L/h | 18 W | 83 L/h per W | $28 |
| Nyos Quantum 120 | 500 L/h | 8 W | 63 L/h per W | $13 |
| Reef Octopus Classic 110-INT | 420 L/h | 9 W | 47 L/h per W | $14 |
| Red Sea RSK-300 | 500 L/h | 12 W | 42 L/h per W | $19 |
| Reef Octopus Classic 150-INT | 720 L/h | 18 W | 40 L/h per W | $28 |
| Tunze 9004 | 150 L/h | 4 W | 38 L/h per W | $6.31 |
| Bubble Magus Curve 5 | 300 L/h | 8 W | 38 L/h per W | $13 |
| Reef Octopus Regal 200-INT | 1,500 L/h | 40 W | 38 L/h per W | $63 |
| Simplicity 240DC | 660 L/h | 18 W | 37 L/h per W | $28 |
| Reef Octopus Regal 150-INT | 900 L/h | 25 W | 36 L/h per W | $39 |
| Bubble Magus Curve 7 | 520 L/h | 16 W | 33 L/h per W | $25 |
| Simplicity 120DC | 360 L/h | 17 W | 21 L/h per W | $27 |
| Tunze 9004 DC | 200 L/h | 10 W | 20 L/h per W | $16 |
Air and watts from the makers at full power; a year at 24 h a day and $0.18/kWh. DC models at their maximum — turned down they draw less and pull less. The Nyos rows are the maker's unverified maximums.
How protein skimmers fail
- The break-in that never ends. A new acrylic body has a film on it that kills foam for one to three weeks; people return skimmers in week one. Run it wet, ignore the cup, and wait. If it still makes nothing at a month, the water level or the air line is the problem, in that order.
- The air line. A skimmer's air figure assumes an open intake. A silencer half-blocked with salt creep, a kinked line, or an air valve someone turned down "to stop it overflowing" cuts the air draw, and the skimmer quietly becomes the size below. Pull the line off and listen once a month; clean the silencer when the pitch changes.
- Calcium on the wheel. The needle or pinwheel runs in saturated water and grows a crust; air draw creeps down over months. Vinegar, twenty minutes, twice a year. A DC controller that shows the pump's power makes the creep visible; on an AC pump the cup going dry is the first sign.
- The water level moved. An ATO that drifts, a return pump turned down, a new baffle: the skimmer that was tuned is now an inch deep or shallow, and the depth table says what that does. The permanent fix is a stand and a mark on the sump glass.
- The pump. On a Reef Octopus or a Sicce-pumped body it is a stocked part; on a house brand it is a search. The warranty on the cards is the warranty on the pump, because nothing else on a skimmer wears out.
What we'd skip
- Buying by the box's "heavy" figure. The table above scores it: 2× the air on the Curve 7, 2.1× on the Simplicity 240DC. Buy by the air column; if the maker prints no air figure, walk on.
- Sizing on the display alone. The sump is 22 % of the water on a normal system, and the box did not count it.
- A body whose depth window your sump cannot reach. A stand fixes deep; nothing cheap fixes shallow. The 6 in column is the one to read for an all-in-one.
- Three sizes over "to be safe." Over 4.5 L/h per liter the tank cannot feed the foam, and an AC skimmer at that size is a weekly tuning job. One size over, or a DC pump turned down.
- A skimmer with no air figure at all. A listing that prints gallons and no liters per hour has told you nothing you can check — and the makers who measure print the number.
Common questions
Do I need a protein skimmer at all?
Not on a lightly stocked tank with a refugium and a water-change habit — plenty of soft-coral and LPS tanks under 40 gallons run without one. What a skimmer does is pull dissolved organics out before bacteria turn them into nitrate and phosphate, and add oxygen while it does it; the more fish you feed, the more that matters. The honest test is your nitrate trend: if water changes alone hold it where you want it, a skimmer is optional. If you are chasing it, the skimmer is cheaper than the water.
Is a bigger skimmer better? Can I oversize it?
Up to a point. A skimmer a size over what the air rule asks for runs with headroom and tunes easily; a skimmer three sizes over never sees enough organics to hold a stable foam head, so it either sits dry or dumps a cup of water when you feed. The "big" mark in the tables — over 4.5 L/h of air per liter of system water — is where that starts. A DC skimmer moves the line, because you can turn the pump down; an AC skimmer at three sizes over is a mistake you tune every week.
Why does my skimmer overflow after a water change or a feed?
The foam head is set by the balance of air, water level and surface tension, and the last one changes every time you add anything organic — food, amino acids, a fresh bag of carbon, a dead snail, new salt water with a different surfactant load. Skimmers go wild for a day after a water change and calm down. The permanent version of the problem is a sump level above the body's window: the foam column starts higher and the cup is nearer the water, so every small change tips it over. The depth table above says how much of a stand fixes that.