Aquarium Stocking Methodology & Editorial Standards

Last updated: October 6, 2026

How the calculator works

The calculator runs in the browser. It is a planning estimate, not a measured result. The same functions are on the homepage.

Stocking points: a small fish is 1 point, a medium fish is 3, a large fish is 8, and an XL fish is 14. A normal setup allows 1 point per gallon. A heavy-stock setup allows 0.6 points per gallon. Capacity is that rate times the gallons, rounded. The percent is points divided by capacity. Comfortable is at or under 80 percent. At capacity is above 80 and at or under 100. Overstocked is above 100.

Heater watts use 2.5, 3, 4, or 5 watts per gallon, set by the temperature rise, then rounded up to a standard size. For a rise above 9°F and at most 15°F, the rate is 4 watts per gallon. A 20-gallon tank from 68°F to 78°F is 100 watts, one heater. A 55-gallon tank from 68°F to 78°F is 250 watts, and the two-heater note is 125 watts each. Tanks of 40 gallons and up get that two-heater note.

Filter ratings use 4 turnovers an hour for light, 5 for normal, and 7 for heavy, then this calculator's 20 percent step, rounded up to the next 5 gallons per hour. On this calculator, 29 gallons at the normal level is 5 turnovers an hour, 145 gallons per hour ideal, and a rating of 175. That step is this site's allowance, not a manufacturer measurement.

Water changes use the rise, ceiling, and tap you enter. On this calculator, a weekly nitrate rise of 20 ppm, a ceiling of 40 ppm, and tap water at 5 ppm returns a 60% water change. The plateau at that change is 38 ppm. Those three figures are example inputs, not a test from a tank.

Where the numbers come from

The point rules, watts-per-gallon steps, and turnover rates above are the rules this site states on the homepage. They are planning estimates for a cycled freshwater tank, not a published standard.

The heater and filter size chart is separate. Values are copied exactly as published. Every row links its source document. The access date is October 6, 2026. A missing value says "not listed". Nothing on that chart is estimated, and makers are not averaged.

Species and care pages link the manufacturer, extension, or profile page they use. Those links sit on the page that uses them.

How pages are written

Page text is drafted with AI assistance from the cited sources. Compiled with AI assistance from the sources below. Spot an error? Email jpanasuk@gmail.com.

Built and owned by Jeremy Panasuk, New Auburn, WI.

Do not present as veterinary advice. An aquatic veterinarian is the person to call when fish are sick.

Affiliate policy

As an Amazon Associate I earn from qualifying purchases. The Amazon links below are affiliate links; they don't change the math.

This site is in the Amazon Associates program. The tag on those links is generatorsi0d-20. The disclosure sits before the first affiliate link on each page. The links do not change calculator output. This site does not sell paid placements.

Corrections

Spot an error? Email jpanasuk@gmail.com with the page URL.

Corrections log

• Oct 6, 2026: the homepage water-change answer was corrected so a 20 ppm weekly rise, a 40 ppm ceiling, and 5 ppm tap reads as a 60% change, with a plateau of 38 ppm.

Sources

• Homepage calculator, including the methodology note and the worked table.
• Heater and filter size chart, accessed October 6, 2026.
• About, for who owns the site and how pages are drafted.