Gear
Buy the right size, once.
Most "best of" lists are a bestseller page with adjectives. These are built the other way round: the calculator works out what size your tank needs, and the gear page says which product is right at that size — with the specs that decide it, and the ways each one fails.
Which heater is right for your tank by physics, not the box — and how hot each one cooks the tank if it sticks on.
Sized by the Heater Wattage calculator Read the comparison → Best canister filtersRated flow against the flow you actually get with media in, the media volume that is the real spec, and what each one costs to run for a year.
Sized by the Filter Size calculator Read the comparison → Best return pumpsWhat each pump really delivers at a real head, from its curve — and the watts it draws to do it, DC against AC.
Sized by the Return Pump Sizing calculator Read the comparison → Best protein skimmersThe box's "up to 150 gallons" against the two numbers that decide it: the water a reef actually holds with its sump, and the air the skimmer pulls through it — plus the sump depth each body needs.
Sized by the True Water Volume calculator Read the comparison → Best reef LED lightsGallons are the wrong unit for a light: the fixtures each line takes to cover your tank's footprint for LPS and for SPS, what that really costs with the mounts, and which makers publish a PAR figure at all.
Sized by the Tank Volume calculator Read the comparison → Best RO/DI systemsEach system's all-in cost per gallon at your tap TDS — membrane rejection and DI capacity are the specs that decide it — and what its GPD really makes in cold water at your pressure.
Sized by the DI Resin Life & RO/DI Cost calculator Read the comparison →How these pages are written
Physics first. Each page starts from the engine behind the matching calculator, so when it says a 100 W heater is right for a lidded 20 to 40 gallon tank, that is heat loss through glass at a 10 °F gap, not a number on a box. Failure modes are the review. What a product does when it breaks decides whether it belongs on a tank you care about, and it is the part every spec sheet omits. Cheap wins are named. When the right answer is a $35 controller rather than a $90 heater, the page says so.
Some links on these pages are affiliate links and earn us a commission at no cost to you; the picks are made on specs, never on commission. How that works.