Free tools
Freshwater keeper tools
Calm, honest little helpers for the questions that keep keepers up at night — starting with the water. Free, no sign-up, nothing saved.
Stocking & tank-size calculator
The number one beginner mistake is too many fish in too little water. Tell us your tank and your wish-list — we'll check each fish against its fact-checked minimum tank and group size, flag clashes, and estimate how full the tank is.
Cycling tracker
The nitrogen cycle is the step nobody explained. Log your ammonia, nitrite and nitrate and we'll tell you which stage you're in, what's normal, and when it's finally safe to add fish. Saves in your browser.
Water-parameter interpreter
You tested the water — now what do the numbers mean? Enter your ammonia, nitrite, nitrate and pH and get a plain-English read on whether your fish are fine or your water needs work.
Tankmate compatibility checker
Will these fish get along? Tick any combination and we check every pair for temperature clashes, predators vs shrimp, the betta solo rule and water-hardness mismatches — before you buy, not after.
Which fish is right for me?
Not sure where to start? Tell us your tank size, whether it's heated, and your water hardness — and get matched to beginner-friendly fish that actually fit, each with a fact-checked guide.
Compare two fish
Torn between two fish? Pick any two and see them side by side — difficulty, tank size, water parameters, temperament, diet and lifespan — straight from our fact-checked care sheets, so it can never contradict the full guide.
All free, no sign-up, nothing saved. More species and tools as Finfern grows.