New on the App Store iOS 17+

Your tank crashed.
Your notes didn’t
tell you why.

FishTank Diary logs every pH, ammonia and nitrate reading, reminds you before a water change is overdue, and shows you the thirty days that led to today.

Download on the App Store See how it works
Free for one tank No account Works offline
What is FishTank Diary?

FishTank Diary is an offline aquarium logbook for iPhone and iPad. You log water tests — pH, ammonia, nitrite, nitrate, temperature — record water changes, filter cleaning, siphoning and feeding, and the app keeps a dated history per tank with reminders for whatever is due next.

No account, no cloud, no subscription. One tank free, forever; a one-time unlock for multiple tanks, trends and CSV export.

What you can log → How it compares →
No account No email, no sign-up, no password to forget.
Works offline Every log is written to your device first.
No tracking The App Store privacy label reads: data not collected.
Features

A logbook built around the test, not around the app

Five fields, one screen, twenty seconds. Everything else — reminders, trends, export — exists because the entry was easy enough that you actually made it.

Water Test Log Free

pH, ammonia, nitrite, nitrate, temperature and any custom reading — attached to the tank it came from, dated, and searchable.

Learn more →

Maintenance Reminders Free

Water changes, filter cleaning, siphoning, top-offs and dosing — scheduled per tank, with overdue work surfaced on the Today screen.

Learn more →

Multi-Tank Dashboard Pro

Track multiple tanks with separate logs, schedules and parameters — plus an All Tanks overview of what needs attention today.

Learn more →

Water Trends Pro

7, 30 and 90-day charts for pH, nitrate, temperature and every other parameter you log — one line per tank.

Learn more →

Turtle Tank Log Free

Turtle tanks are messy, heavily filtered and water-changed far more often. Log water parameters, siphoning and basking setup in the same place.

Learn more →

Offline & Account-Free Free

Every log is written to your device. No sign-up, no email, no analytics — the App Store privacy label says data not collected.

Learn more →
See all features
How it works

Three taps from test tube to history

The app does not ask you to configure anything before it is useful. Open it, log, done.

01

Log the reading

Pick the tank, tap the parameters you tested, type five numbers. Last week’s values are pre-filled so you only change what moved.

02

Set what is due next

Water change, filter rinse, siphon, feeding — each tank carries its own schedule. Overdue work stays on the Today screen until you confirm it.

03

Read the trend, not the number

7, 30 and 90-day charts per parameter. Nitrate climbing three weeks in a row is a different problem from nitrate being 20 once.

Full walkthrough →
Why small tanks

Twenty litres has no margin for a missed week

In a nano or 5-gallon tank, the same waste dissolves into a quarter of the water. Ammonia shows up faster, evaporation changes hardness faster, and the temperature follows the room. The maintenance rhythm is the whole hobby at that size.

  • Daily-friendly logging. A five-field entry you will not skip on day nine of a cycle.
  • Reminders sized to the tank. Weekly for a stocked 5-gallon, fortnightly for a planted 20.
  • Top-offs tracked separately. Because refilling evaporation is not a water change.
  • Turtle tanks included. Siphoning and frequent partial changes are scheduled tasks, not notes.
Nano tank guide 5-gallon setup
// 5G Shrimp · 2026-10-28 19:42 { "tank": "5G Shrimp", "volume_gal": 5, "ph": 6.8, "ammonia": 0, "nitrite": 0, "nitrate": 10, "temp_c": 24.1, "note": "30% change, molts visible" } // reminder: siphon → in 3 days // trend: NO₃ 14.2 avg / 30d ↓ improving
Knowledge base

The parts of the hobby worth writing down

Guides

Cycling, ammonia and water changes

The three things that decide whether a new tank survives its first two months.

4 guides → Tank setups

5-gallon, 10-gallon, nano

Stocking plans and maintenance schedules that match the volume you actually have.

Browse setups → Species

Care sheets that stay small

Chili rasbora, honey gourami, pygmy corydoras, otocinclus, ember tetra.

Care sheets → Tools

Water change calculator

Turn a nitrate reading into a percentage, and see what a fixed schedule really does.

Open tools →
Compare

How FishTank Diary compares

A logbook competes with a notebook, a spreadsheet and a note on your phone. Here are the honest side-by-sides.

Paper logbookSpreadsheetNotes appGeneric aquarium apps
See all comparisons
Pricing

Free for one tank. $3.99 once, forever

No subscription, no ads, no data collection. The unlock is a purchase, not a rental.

Free
$0forever
  • One tank, unlimited logging
  • Water tests, maintenance and feeding log
  • Reminders and the Today dashboard
  • Offline, no account required
Pro · one-time
$3.99once
  • Unlimited tanks + All Tanks overview
  • 7 / 30 / 90-day trend charts
  • CSV export of your full history
  • Restore on any device, no subscription
Get the app
FAQ

Frequently asked questions

What is FishTank Diary?
FishTank Diary is an offline aquarium logbook for iPhone and iPad. You log water tests (pH, ammonia, nitrite, nitrate, temperature and any custom parameter), record maintenance like water changes, filter cleaning, siphoning and dosing, and add feeding entries. The app keeps a dated history per tank, shows a Today dashboard of what is due or overdue, and — with the one-time Pro unlock — charts trends over 7, 30 or 90 days, tracks multiple tanks and exports everything to CSV.
Do I need an account or an email address?
No. There is no sign-up, no email, no password and no cloud account. You open the app and start logging. That is also why the App Store privacy label reads data not collected.
Does it work without an internet connection?
Yes. Every log is written to your device, and reminders are scheduled locally, so the app works in a basement fish room or anywhere with no signal.
Which water parameters can I log?
pH, ammonia, nitrite, nitrate and temperature are built in. You can add custom parameters — GH, KH, salinity, phosphate, CO₂, TDS — and they behave exactly like the built-in ones.
Can I use it for a turtle tank?
Yes. Turtle tanks are treated as a first-class case rather than an afterthought: you can log frequent partial water changes, siphoning, filter services and basking bulb changes on the same timeline as your water tests.
How much does Pro cost?
Pro is $3.99 as a one-time purchase — not a subscription. It unlocks unlimited tanks, the All Tanks overview, 7/30/90-day trend charts and CSV export. The free version keeps one tank with unlimited logging, with no time limit.
How is this different from a notebook or a spreadsheet?
Capture speed and reminders. A structure that stays consistent, so the data is comparable months later. Per-tank schedules that surface overdue work on the Today screen. And CSV export, so the history is still yours to take elsewhere.
Does it sync between my iPhone and iPad?
Device sync is not part of the current release. The app is local-first by design; use CSV export if you need to move history between devices.
Does the app give medical or veterinary advice?
No. It records what you measured and flags readings outside the range you set. It does not diagnose disease or recommend medication — for that, talk to a vet or an experienced keeper.
Download

Your next water change is already scheduled

Open the app, log one test, and the rest — reminders, history, trends — is automatic. Free for one tank, no account.

Download on the App Store Free · No account · Works offline
QR code linking to FishTank Diary on the App Store
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 →