TestwaterAquarium test log for iPhone

Every reading against your tank’s own range.

Type a whole test on one screen, with no limit on readings on any plan. Anything outside your tank’s own range comes first, with up to its last eight readings.

One tank free. Testwater Plus is £1.99 a month or £12.99 a year, and works out reef and planted doses. UK prices; the App Store shows yours.

Coming soon How it compares

iPhone, iOS 26 or later. No account.

After a test

What’s off comes first, with its run.

Any reading outside your tank’s own target range gets a card at the top: the value, Low or High, the change since last time and up to its last eight readings against the band.

Everything in range is a plain row. The starting ranges are a guide, and yours to edit for your livestock.

Log a test

01

A whole test on one screen.

Every parameter you test, with its last reading and its target under it, and Previous and Next on the keyboard. A value outside the range says so as you type.

02

Off the scale? Say so.

When a kit reads below its lowest mark or above its highest, enter it with < or >, and it’s saved that way.

Log a test for Reef 250: eight fields, each with its last reading and target, nitrate 15 ppm marked High and phosphate entered as less than 0.02

Reef dosing, with Plus

01

Copy the label once.

Add your alkalinity, calcium or magnesium product from its label, in the label’s own units. Then set the most it may raise the level in a day; it starts at 1.0 dKH. Testwater has no built-in products and recommends none.

02

The dose, with the working shown.

From your latest test to the middle of your range, split over enough days that it never rises more than the daily limit you set. Check with your test kit before and after dosing.

Reef dosing for Reef 250, in dark appearance: Alkalinity buffer (liquid), current 7.2 dKH low, target 8.5 dKH, 19.5 mL a day for 2 days, with the working shown

Planted tanks, with Plus

Dry fertiliser, in grams per dose.

The Estimative Index worked out for your tank’s volume and how often you dose: potassium nitrate, monopotassium phosphate, potassium sulphate, magnesium sulphate and a trace mix.

Change how many doses a week and every figure follows. Edit a weekly target and it becomes your own schedule.

Tasks

01

Every job on its own interval.

Water changes, filter cleans, tests and doses, each with its own number of days. Late ones say Overdue in words.

02

Done, from the reminder.

A reminder comes on the due day. Touch and hold it and tap Done, and the next one is set. Saving a test ticks off its test task too, and with Plus, so does logging a dose.

Reef 250’s tasks: clean skimmer cup overdue by 1 day, dose alkalinity, replace RO cartridges and a 20% water change due today, and tasks coming up

And the rest

For every tank you keep.

Every tank on one list

Freshwater, planted, marine or pond. Each row says what’s off and what’s due.

Bring your notebook

Import a CSV from a spreadsheet or another app’s export, with a preview before anything changes.

Back up, and undo

Export your readings or a full backup. A restore or an import can be undone.

Your units

Degrees, litres or gallons, and dKH or meq/L, changed in Settings at any time.

Readings with notes

Add a note to a test, and see every reading of a parameter with its own.

How it compares

Doses worked out, with no account.

Set beside AquaticLog, Fishkeeper and Coralog, checked on 19 October 2026.

How Testwater compares

  • Works out your doses, with PlusReef supplements in millilitres and dry fertiliser in grams. None of the other apps here lists a fertiliser calculator.
  • No account to make, like CoralogYour readings stay on your iPhone, in its own backups and in the files you export. Nothing is sent to us.
  • Where others do moreFishkeeper is free for any number of tanks, with an account, and AquaticLog also records your fish and corals.

Plans

One tank free. Plus for the rest.

Free

£0

No time limit

  • One tank, with unlimited readings
  • Charts, tasks and reminders
  • CSV import and export, backup and restore

Testwater Plus

£1.99 a month

or £12.99 a year. No free trial. UK prices; the App Store shows yours.

  • More tanks
  • The reef dosing calculator, for marine tanks
  • The fertiliser schedule, for planted tanks

Dosing is part of Plus on every tank, your free one included.

If Plus ends, nothing is deleted: your oldest tank keeps working as on the free plan, and the others become read-only, with everything still there to export.

Questions

Before your next water test.

Is there a limit on how many tests I can log?

No, on any plan. The free plan is one tank, with every reading you log; Plus adds more tanks.

Does Testwater work out reef supplement doses?

With Plus, yes: alkalinity, calcium and magnesium, from your own product’s label, your latest test and your tank’s volume, with the working shown. Check with your test kit before and after dosing.

Can I use it for a planted tank?

Yes. Tanks can be freshwater, planted, marine or pond, each starting with its own parameters. With Plus, a planted tank gets the dry fertiliser schedule in grams.

Can I bring my old readings with me?

Yes. Import a CSV from a notebook spreadsheet or another app’s export, with a preview first. You can export your readings as a CSV, or everything as a backup, on any plan.

Does it need an account?

No. Your readings stay on your iPhone, in its own backups and in the files you export, and nothing is sent to us.

How much is Testwater?

One tank is free, with no time limit. Testwater Plus is £1.99 a month or £12.99 a year in the UK; elsewhere the App Store shows the price in your currency before you confirm.

TestwaterAquarium test log for iPhone

Log every test. No monthly limit.

Coming soon