Aquarium guides
Short, honest answers to the questions that trip up most new fishkeepers — each one paired with a free calculator.
How many fish per gallon?
Realistic stocking for 10, 20, 29 and 55 gallon tanks — and why "1 inch per gallon" misleads you.
What size filter do I need?
The 4× turnover rule, rated vs real GPH, and a tank-by-tank table.
What size heater do I need?
Watts per gallon, temperature rise, and when to run two heaters.
Filter size chart by tank
GPH for every tank from 5 to 125 gallons, plus a suggested HOB and canister filter per size.