Tools
Two calculators worth bookmarking
Both solve the same problem the app solves in the background: turning a number you measured into a decision you can act on.
Calculator
Water change calculator
Turn your current nitrate reading and a target into a water change percentage — and see what a fixed weekly schedule actually does over four weeks.
Open → CalculatorAquarium volume calculator
Convert tank dimensions to real water volume in gallons and litres — and subtract substrate, hardscape and the gap below the rim.
Open → Download 
The app does the maths for you
Log the reading and the app keeps the percentage, the schedule and the history together — no calculator, no notebook.
Download on the App Store Free · No account · Works offline
Point your camera at the code FishTank Diary is an iPhone and iPad app. Install it now — no account, no email, no setup.
Open the App Store link →
Open the App Store link →