About AquaStock

AquaStock is a free set of tools and plain-language guides for freshwater aquarium keepers. The main tool answers the question every new tank raises and almost every stocking chart answers badly: given this tank, this filter and these fish, is the tank overstocked? Everything runs in your browser. There is no sign-up, no account, and nothing to install.

Why "one inch per gallon" is not good enough

The rule most beginners meet first is one inch of fish per gallon of water. It is wrong in both directions and it is wrong for interesting reasons. Bioload does not scale with length: a six-inch goldfish produces far more waste than six one-inch tetras, because waste output tracks mass and metabolism rather than a linear measurement. The rule also ignores filtration entirely, ignores whether a species shoals and will be stressed in small numbers, ignores adult size in favour of the size at purchase, and ignores tank footprint, which matters more than volume for bottom-dwellers and territorial fish.

Our stocking calculator models bioload rather than length, checks schooling minimums and adult size, and gives a verdict with the reasoning shown instead of a single number you have to trust. Where the answer is genuinely "it depends", it says so.

What is here

Calculators: tank volume converts dimensions to litres and US gallons, including the real water volume once substrate and displacement are considered; heater wattage sizes a heater against your room temperature rather than a generic watts-per-gallon figure; water change works out volumes and schedules; and how many fish per gallon takes on the stocking question directly.

Guides, written for the problems that actually sink a tank: the nitrogen cycle and fishless cycling (the single most common cause of early fish deaths), cloudy water, algae control without chemicals, pH, GH and KH explained, choosing a filter, quarantine tanks, a maintenance schedule, how much to feed, substrate and live plants, schooling minimums, fish that outgrow your tank, aquarium salt myths, and aquariums and power outages.

What this is not

These tools are planning aids, not veterinary advice and not a substitute for testing your own water. A calculator cannot see your ammonia reading, your nitrate trend, or the fish that has been hiding for two days. If livestock is sick, test the water first and consult an aquatic veterinarian or an experienced local shop; if a calculator here and your test kit disagree, believe the test kit. Stocking is also a matter of judgement as much as arithmetic, and a verdict of "fine" assumes maintenance actually happens.

How this site is paid for

AquaStock is free and always will be. It is supported by display advertising, and some outbound links to equipment may be affiliate links, meaning we could be paid a commission at no additional cost to you. We state this plainly because a stocking calculator that quietly recommends whatever pays it is worse than no calculator, and because you deserve to know our incentives before weighing our advice. No commercial arrangement changes what a calculator computes or what a guide says.

Who runs it

AquaStock is operated by Crossroads Technologies, LLC, a small independent publisher of free web utilities. We are hobbyists rather than ichthyologists, we build the tool we wanted when we started, and we would rather be corrected than be confidently wrong. Corrections, species we have modelled badly, and requests for tools we have not built are all welcome via the contact page.