StablereefOne quick session
A big number pad, your last value on every step, one summary where you can undo any single reading.
Free forever core · works offline
Keep your reef stable.
Log a full water test in about 30 seconds — and catch a rapid swing the moment you save, while you’re still at the tank.
iPhone & Android · No account · No ads
The anti-swing warning
Corals don’t crash on a number. They crash on the swing.
When you save a reading, Stablereef compares it to your last one — and tells you straight away if the change is too fast, or the value is out of range. Drag the slider and see it.
Display Reef 75G · AlkSafe range 7.0–12.0 dKH
Last test: 8.6 dKH · 20 hours ago
dKH
Illustration using the app’s default Alk settings (safe range 7–12 dKH, 1.0 dKH per day). Both are tunable in the app. Reference only — husbandry calls are yours.
Made for the tank-side
Everything you need to log, nothing you don’t.
Fast to use with wet hands, honest about your numbers, and yours to keep.
Anti-swing alerts
Flags a rapid change or an out-of-range reading the moment you save — with allowance for the time since your last test.
Your kit’s units
dKH, meq/L or ppm. ppm PO4 or ppb P. °C or °F. ppt or SG. Enter what your kit shows — no converting in your head.
Cycling mode
Starting a new tank? Ammonia and nitrite come first, high readings get a calm “this is expected” note, and you’re told when the cycle looks done.
Trends with a safe band
7, 30 and 90-day charts with the stable range shaded in, so you can tell real drift from noise.
Bring your log. Take it back.
Free CSV import from a spreadsheet or another app, and CSV / JSON export any time. We don’t hold your data hostage.
Inside the app
Calm, clear, and quick.
Swipe through the screens you’ll use every week.
No account. No cloud. No ads.
Everything you enter stays on your device. We have no servers that receive your aquarium data.
Works offline
Log right next to the tank, no signal needed.
Your data, always yours
Free CSV / JSON export and automatic local backups. No paywall on your own data.
Anonymous counts only
The only thing the app sends is anonymous usage counts — no personal data, no IP — and you can switch it off in Settings.
Questions
Good to know
Is Stablereef free?
Yes. Logging is unlimited, and reminders, CSV import and CSV / JSON export are free — there’s no paywall on your own data.
Do I need an account?
No. There’s no sign-up and no cloud. Everything stays on your device, and the app works fully offline.
Can I bring my existing reef log with me?
Yes. Import any CSV — from a spreadsheet or another aquarium app — with automatic column detection, unit conversion and a preview before anything is written.
Which parameters and units does it support?
Alkalinity, calcium, magnesium, nitrate, phosphate, salinity, pH and temperature, plus ammonia and nitrite when you need them. Enter values in the units your test kit shows: dKH, meq/L or ppm for alkalinity; ppm PO4 or ppb P for phosphate; °C or °F; ppt or specific gravity.
How does the anti-swing warning work?
When you save a reading, Stablereef compares it to your last one — allowing for the time since that test — and flags a rapid change or an out-of-range value. Safe ranges and thresholds are tunable. It’s a reference only; husbandry calls are yours.
How do I delete my data?
Your data lives on your device, so you stay in control. The data deletion page explains the steps.
Keep your next test stable.
Free to start, nothing to sign up for. Your reef log is ready in a minute.