01 - log
Type in what you tested.
Pick a tank, drop in pH, temp, NO₃, KH, whatever you ran today. Auto-saves. Yesterday's reading sits one line above for sanity.
Calmer water, sharper readings.
Four small calculators and a quiet little journal - for the days you want to think about your tank without thinking about your tank.
1,000+ keepers
2,800 tanks logged
4 tools always free
0 ads ever
pH · live
6.82
↑ 0.04 over 24 h · within target
Temp · 24 h
24.1°C
stable · 23.9 - 24.3
CO₂ · diffuser
28.4mg/L
drop checker · green
Free · no account needed
Four calculators that do the maths so you don't have to.
The boring chemistry - converted, compensated, sanity-checked. Each tool runs in your browser, no sign-up required.
01 / 04
Tank volume
Length × width × height, minus substrate, with glass-thickness suggestion. Litres, gallons, surface area.
Open tool
02 / 04
Water change
Grams of GH+ and KH+ to add to your RO/DI for a perfectly remineralised change - TDS computed.
Open tool
03 / 04
Fertilization
Dry-salt dosing for KNO₃, KH₂PO₄, K₂SO₄ and friends - EI, PPS-Pro, or your own profile.
Open tool
04 / 04
CO₂ concentration
Dissolved CO₂ from pH and KH, with temperature compensation. Returns drop-checker colour, too.
Open tool
How it works
Three quiet habits, one healthier tank.
We won't tell you to log every parameter every day. We will make it easy to log the ones you want, the days you remember.
02 - see
Watch the line, not the numbers.
Trends over 7, 30, 90 days, with target bands so a wobble in pH looks like a wobble, not an emergency.
03 - remember
A photo, a note, a milestone.
Document the slow win - the carpet filling in, the first berried shrimp, the day you finally beat the diatoms.
Inside the app
It looks like this. You'll spend two minutes here a week.
app.aquarium.tools/dashboard
Tanks online
4 / 4
Open tasks
5
Logs · 30 d
142
RO water
68 L
pH · last 30 days
target 6.5 - 7.5
7d · 30d · 90d
CO₂
28mg/L
From the community
People who keep tanks that don't keep them.
“
I stopped guessing. Two weeks of logs and the GSA outbreak made sense - I'd been blowing past my phosphate target every Sunday.
H
Hana K.
Planted · 90 L · 14 months
“
The CO₂ calculator alone saved me a yellow drop checker and a panicked livestock count. Refreshing to find a tool that just… does the maths.
A
Aurelia P.
Reef · 240 L · 3 years
“
I keep four tanks across two flats. The schedule view on Sunday morning is the closest thing I've found to peace in this hobby.
M
Marco S.
Mixed · 4 tanks · 5 years
FAQ
Reasonable questions, reasonable answers.
Are the calculators really free?
Yes - the four tools on this site have been free since 2012 and aren't going anywhere. You don't need an account to use them. Creating one lets you save tanks, log readings, and keep a photo journal.
Why no password? What is a magic link?
When you sign in, we email you a one-time link. Click it, you're in. No passwords to remember, no passwords to lose. Less surface for bad days.
Do I have to be a reef-keeper?
Not at all. The app is built around the boring maths every aquarium has - salt or no salt. Reef, planted, shrimp, brackish, quarantine: all welcome.
Where is my data stored?
In a European data centre. We don't sell it, we don't share it, and you can export the lot as JSON or CSV any time. There's also a delete-account button that actually deletes your account.
How accurate is the CO₂ calculator?
It uses the Krib equation - CO₂ = 12.839 · KH · 10^(7 − pH) - with a Henry's-law temperature correction. Accurate when your water isn't loaded with phosphate buffers or organic acids; otherwise treat the number as a good guide, not gospel.
Is there a mobile app?
The web app is the mobile app. Add it to your home screen on iOS or Android and it behaves like a native app - including the bottom nav you're probably looking at right now.
Less guessing. More keeping.
Set up your first tank in under two minutes. Free for as long as you want.