AqAdvisor alternative: a mobile-friendly fish stocking calculator

Published 2026-10-13 · Updated 2026-10-13 · AqAdvisor details checked October 2026

FishFits is a free, mobile-friendly alternative to AqAdvisor. Like AqAdvisor, it estimates how full your tank is, finds water conditions every fish can share and warns about bad matches. It differs by showing waste and swimming space as two meters, suggesting fish that would still fit, and listing the sources behind each species. AqAdvisor covers far more species (917 vs 150) and has a saltwater version.

AqAdvisor is one of the best-known aquarium stocking calculators, and its how-it-works article dates back to 2010. It deliberately avoids the old “one inch of fish per gallon” rule and instead weighs each species’ size and bioload, along with traits such as aggression, group size and water needs.

FishFits takes a similar approach and builds it for phones, with its formulas published and sources listed for every species. This page compares the two as fairly as we can. Both tools are free, and you can use both.

Feature comparison (as of October 2026)

We checked every AqAdvisor detail below on aqadvisor.com on 13 October 2026, including test runs of its calculator. Websites change, so if something here is out of date, let us know and we’ll fix it.

AqAdvisor and FishFits features compared
Feature	AqAdvisor	FishFits
Price and sign-up	Free. The calculator works without an account.	Free. No account, no sign-up.
Species	917 species in the freshwater calculator, plus a separate Saltwater Advisor (79 species).	150 freshwater fish, shrimp, snails and other invertebrates. Freshwater only.
Finding a species	A scrollable list showing common and scientific names, with search on both and an option to sort by scientific name.	Type-ahead search on common names, other names and scientific names.
Tank input	Presets from 2.5 to 500 gallons (some branded tanks included), or your own length, depth and height.	Common sizes or any volume in gallons or litres. Tank length is optional and used for active swimmers.
Filter input	Choose from more than 360 named filter models with their rated capacity built in, or enter your own. Two filter slots by default, and you can add more.	Optional: type your filter’s flow in GPH or L/h.
Main results	Stocking level %, filtration capacity % and a suggested weekly water change %. Space warnings appear when fish may outgrow the tank or need more territory than it has.	A waste meter and a space meter. The higher one is your stocking level.
Shared water conditions	Shows the temperature, pH and hardness range that suits all selected species, and lists each species’ range when they don’t overlap.	Shows the shared temperature, pH and hardness range, and flags any that don’t overlap.
Warnings	Warnings that name the species, covering aggression, fin nipping, predation, group size, outgrowing the tank and water, plus care notes such as fish that jump.	Warnings that name the fish and say why (predation, fin nipping, aggression, group size, tank size, water), each marked won’t work, risky or good to know.
Juvenile sizes	Yes. A juvenile mode lets you enter current sizes and compare them with adult sizes.	No. We always use adult size, because shop-size fish grow.
Help choosing more fish	A button that shows only species your tank is big enough for.	Suggests species that fit the space left and get along with your fish, with the stocking level each would give.
How it works	A “How does AqAdvisor.com work?” article (last updated April 2010) listing the species traits it weighs, plus a help page.	A methodology page with the formulas and thresholds we use.
Sources for species data	Not listed in the calculator results.	Every species page lists its sources and the date it was last reviewed.
Saving and sharing	Bookmarkable link, copy/paste-friendly text and an image of your stocking.	Share link, print view, and save to My tanks in your browser.
Units	Gallons or litres, inches or cm, °F or °C.	Gallons or litres, inches or cm. Temperatures shown in °F and °C.
Other tools on the site	Saltwater Advisor, sample stocking plans and beginner articles (cycling, water chemistry, algae eaters and more).	Compatibility checker and chart, tank mates pages, tank size pages, 8 calculators and care guides.
Tank log	None that we found.	My tanks: water test log, cycle status and maintenance reminders, stored only in your browser.
On a phone	A fixed-width desktop layout (about 1,050 px), so on a phone you usually zoom and scroll.	Designed for phones first and works at 360 px wide.

Where AqAdvisor is the better choice

Rare or unusual species. With 917 species in its freshwater calculator, AqAdvisor is more likely to list an uncommon fish we don’t cover yet.
Saltwater tanks. AqAdvisor has a separate Saltwater Advisor. FishFits is freshwater only.
Picking a filter by model name. AqAdvisor lets you choose from a long list of filter models and combine several. With FishFits you type the flow rate from the box or manual.
Planning with young fish. AqAdvisor’s juvenile mode lets you enter your fish’s current sizes and compare today’s numbers with their adult sizes. We only plan for adult size.
A water change figure for your fish. AqAdvisor suggests a weekly water change percentage based on your stock. Our stocking calculator doesn’t. Our water change calculator works from your nitrate readings instead.

What FishFits does differently

Waste and space are two separate meters

Fish need clean water and room to swim. A stronger filter, live plants and more water changes help with the first, but nothing except a bigger tank helps with the second. So the stocking calculator shows a waste meter and a space meter, and your stocking level is whichever is higher. Filter flow and live plants only ever move the waste meter.

AqAdvisor handles filters differently: it keeps them out of its stocking level and reports filtration as a separate number. In our test, swapping a small filter for a much larger one on 30 neon tetras in a 20 gallon long changed its filtration capacity figure (59% to 324%) but not its stocking level (83%). It also warns when territorial fish may need more space than the tank has. Both tools make the same point: a bigger filter doesn’t make room for more fish. FishFits shows both limits as meters on every result and labels your stocking level with the one you hit.

Compatibility you can look up on its own

In the calculator, each warning names the fish involved and says why: one can eat the other, one nips fins, the water ranges don’t overlap, or a group is too small. Outside a full plan, you can check any pair in the compatibility checker, scan the full compatibility chart, or start from a single fish on its tank mates page, such as neon tetra tank mates.

Sources you can check

Each of our 150 species pages lists the sources behind its numbers (adult size, minimum tank, temperature, pH, group size) and when it was last reviewed. The rules behind every result are on our methodology page, including the formulas and the thresholds for each warning.

More than one calculator

Besides stocking, there are tank size pages with stocking ideas for common tanks, and 8 calculators for volume, tank weight, substrate, heater size, filter flow, water changes, CO2 and unit conversion. My tanks keeps a water test log and maintenance reminders in your browser. Nothing is uploaded and there is no account.

Which one should you use?

If your fish are in our database, start with FishFits for a plan that’s easy to read on a phone, with sources behind every species. If you keep a saltwater tank, a rare species we don’t list yet, or young fish you want to plan around, AqAdvisor is the better fit. Either way, treat any calculator as guidance, not a guarantee: leave some headroom below the limit, add fish slowly, and test your water. Our guide to how many fish per gallon explains why simple rules fall short, and how to cycle a fish tank covers the step most new tanks skip.

Frequently asked questions

Is there a free alternative to AqAdvisor?

Yes. FishFits is a free stocking calculator with no account. It checks 150 freshwater species for waste, swimming space, shared water conditions, compatibility and group size, and says why each warning appears.

Is AqAdvisor still accurate?

AqAdvisor still works (we tested it in October 2026) and is a useful first check. Like any calculator, it gives estimates rather than guarantees. Its own site says it can’t promise that species will get along, recommends that new fishkeepers stay under 100%, and asks you to research each species before buying. That’s good advice for any calculator, including ours.

Does a bigger filter let me keep more fish?

Only up to a point. Better filtration helps the tank handle more waste, but it never gives fish more room to swim. FishFits shows waste and space as two meters for this reason, and a bigger filter only moves the waste meter. AqAdvisor makes the same point by keeping filtration out of its stocking level.

Why does FishFits have fewer species than AqAdvisor?

We add a species only after checking its care data against at least two reputable sources and listing them on its page. We started with the freshwater fish and invertebrates people ask about most and add more over time.

Can I use FishFits on my phone?

Yes. Every page and tool is designed for small screens first. Plans saved to My tanks stay in that browser, and you can download a backup to move them to another device.

Sources

AqAdvisor is an independent website. FishFits is not affiliated with or endorsed by it.