How TankStarter Works
Everything on this site is an estimate worked out from published care guidelines. We have not kept or tested these fish or products ourselves. Here is how each number is produced, so you can judge it.
Stocking level
Each species has a stocking weight based on its adult length, adjusted for body mass and how much waste it makes. A slim one-inch tetra counts far less than a goldfish of the same length would. The weights of all your fish are added up and compared with the tank's capacity.
Small tanks get less capacity per gallon: 70% for 5 gallons, 75% for 10 and 90% for 20. Water quality swings faster in a small volume, so there is less room for error. Up to 90% is shown as good, 90 to 100% as full, and anything above as overstocked.
This is a rule of thumb. Real capacity also depends on filtration, live plants, how often you change water and how much you feed.
Compatibility checks
- The tank is at least the minimum size published for each species.
- Schooling and social species are in a group of at least their minimum size.
- Every species shares a temperature range the others can live in.
- Known fin nippers are not paired with long-finned fish.
- Fish big enough to eat very small fish or dwarf shrimp are flagged.
- Territorial surface fish, such as bettas and gouramis, are not doubled up.
Individual fish vary. A combination with no warnings can still go wrong, and some flagged combinations work in a large, well-planted tank.
Equipment sizing
- Heater: 3 to 5 watts per gallon for each 10°F the water must be held above room temperature, rounded up to a standard heater size. Small tanks use the higher figure. If the room is within 2°F of the target, no heater is listed.
- Filter: a flow rate that turns the tank over about 5 times an hour, 4 for fish that dislike current, and 6 for heavy waste loads.
- Substrate: the weight needed for a 1.5 inch layer over the tank's footprint, at about 100 pounds per cubic foot.
- Water conditioner: shown at the common strength of 1 mL per 10 gallons. Products differ, so the label on your bottle is what counts.
Where the fish data comes from
Tank sizes, temperatures, group sizes and adult sizes are the ranges commonly published in aquarium care sheets and hobbyist references, such as Aquarium Co-Op care guides, Aqueon care sheets and Seriously Fish species profiles. Where sources disagree, we use the more cautious figure: the bigger tank and the bigger group.
Tank dimensions and filled weights are the usual figures for standard glass aquariums and vary a little between makers.
What this site can't tell you
- Whether your tank has finished cycling. Only a water test kit can.
- Your tap water's hardness and pH, which matter for some species.
- Which specific product is best. We link to Amazon searches, not to products we have tested.
How this site makes money
As an Amazon Associate, TankStarter earns from qualifying purchases. If you buy through a link here, the price is the same for you. We don't show prices or ratings; check Amazon for those. Recommendations come from the sizing rules above, not from which product pays more.