Reef Monitor: free saltwater aquarium parameter tracker for iPhone

Q: Is Reef Monitor really free?

Yes. Reef Monitor is 100% free with no in-app purchases, no subscription, no premium tier, and no ads. There is nothing locked behind a paywall.

Q: How do I export my data?

Go to Settings and tap Export CSV. The file is shared through the standard iOS share sheet. You can save it to Files, email it, or open it in any spreadsheet app. The format is importable back into Reef Monitor.

Q: Which languages does Reef Monitor support?

15 languages: English, French, German, Spanish, Portuguese, Italian, Dutch, Russian, Japanese, Korean, Chinese, Arabic, Hindi, Turkish, and Polish. The app auto-detects your device language.

Made for the way you keep reef.

No feature is locked. No data leaves your device. Designed by a nano-reef keeper who got tired of spreadsheets.

Built-in timers

Salifert kit timers

Nitrate: 30-second shake plus 3-minute wait. Phosphate: 30-second shake. Countdowns with haptic feedback. No more squinting at the kitchen timer with wet hands.

SPS signal

Alkalinity consumption rate

Linear regression on your alkalinity history surfaces the dKH/day your tank is consuming. The SPS health signal nobody else surfaces this clearly.

Automatic

NO3:PO4 ratio

Reef Monitor watches your nutrient ratio and warns you the moment it drifts into nuisance-algae territory. Same for the Ca/Alk/Mg ionic balance.

15 parameters

From nano to SPS

Temperature, salinity, pH, alkalinity, calcium, magnesium, potassium, strontium, iodine, boron, nitrate, phosphate, ammonia, nitrite, silicate. Enable only what you test.

Multi-tank

Every tank, one app

Unlimited tanks. Each with its own readings, thresholds, doses, and water changes. Switch in one tap from any screen.

Correlated

Dosing and water changes

Log Kalkwasser, 2-part, All-for-Reef or any custom product. See dose markers on the trend charts they affect. Water changes overlay every chart.

Wet-hands UX

Designed for the dosing station

Large touch targets. Plus/minus steppers tuned per parameter. Haptic confirmation. Last value pre-filled. No keyboards in your way.

100% local

Your data, your device

SQLite local storage. No account. No cloud. No tracking SDKs. No network requests at all. CSV export when you want it.

15 languages

Speaks reef, in your language

Auto-detected from your device. English, French, German, Spanish, Italian, Dutch, Polish, Portuguese, Russian, Japanese, Korean, Chinese, Arabic, Hindi, Turkish.

How Reef Monitor stacks up.

Honest comparison with the most-installed saltwater apps on the App Store, as of June 2026.

	Reef Monitor	Aquarimate	Reef Buddy
Price	Free, forever	$9.99	Free + IAP
Works offline	Yes, fully	Partial	Partial
No account required	Yes	Account	Optional
Built-in Salifert timers	Yes	No	No
Alkalinity consumption rate	Yes	No	In premium
NO3:PO4 ratio detection	Yes	No	In premium
Multi-tank	Yes	Yes	Yes
Languages supported	15	13	6
CSV export	Yes	Yes	In premium
Tracking SDKs / analytics	None	Cloud sync	Some

Frequently asked questions

Answers to the questions reef keepers actually ask before installing.

Is Reef Monitor really free?

Yes. 100% free, no in-app purchases, no subscription, no premium tier, no ads. There is nothing locked behind a paywall. The author runs no server (the app is entirely offline) and the operating cost is zero.

Does Reef Monitor work offline?

Yes. The app makes zero network requests. All readings, dosing entries, and water-change records are stored locally in SQLite on your device. You can use the app in airplane mode.

Does Reef Monitor have Salifert test kit timers?

Yes. The nitrate test has a 30-second shake timer plus a 3-minute wait timer. The phosphate test has a 30-second shake timer. Both run inside the log entry screen with progress bars and haptic feedback on completion.

Can I track multiple tanks?

Yes. Reef Monitor supports unlimited tanks. Each tank has its own readings, alert thresholds, dosing log, and water-change log. Switch tanks in one tap from any screen.

Which parameters can I log?

Up to 15: temperature, salinity, pH, alkalinity, calcium, magnesium, potassium, strontium, iodine, boron, nitrate, phosphate, ammonia, nitrite, and silicate. You can enable only the ones you actually test and hide the rest.

How do I export my data?

Open Settings and tap Export CSV. The file is shared through the standard iOS share sheet. You can save it to Files, email it, or open it in any spreadsheet app. The format is importable back into Reef Monitor.

Which languages does Reef Monitor support?

15: English, French, German, Spanish, Portuguese, Italian, Dutch, Russian, Japanese, Korean, Chinese, Arabic, Hindi, Turkish, and Polish. The app auto-detects your device language; no setup needed.

Is Reef Monitor available on Android?

Not yet. The codebase is cross-platform (React Native via Expo), and an Android release is on the roadmap. iPhone is the current focus.

How is this different from Aquarimate or Reef Buddy?

Reef Monitor is the only app in the category with built-in Salifert kit timers. It is 100% free with no premium tier, while Aquarimate is $9.99 paid and Reef Buddy uses a freemium with subscriptions. Reef Monitor also runs fully offline with no cloud sync, no account, and no analytics. See the comparison table above for the full breakdown.

Track your reef. Beat the drift.

Speaks your language