Free · No account · 5 tools in one

Your planted tank.
One dashboard.

AquaCalc is the complete water chemistry toolkit for planted aquarium keepers — CO₂ monitoring, RO mixing, fertiliser dosing, water change planning and safety alerts, all in one free, science-backed dashboard.

Try the full toolkit → See all tools
8
Integrated tools
30+
Chemistry parameters
3
Dosing methods
100%
Free & private
www.aquacalc.uk/dashboard
📊 pH Monitor
28.8 ppm CO₂
At target
💧 RO Mixer
174 ppm
Mixed TDS
🧪 Dosing calc
4.2 ml
KNO3 · EI method · 3× pw
🔄 Water change
34%
83 L to reach 10 ppm NO3
⚠️ Safety
✓ All clear
CO₂ within safe range
🌱 Mode
KH formula
Switch to pH drop for aquasoil
📊 pH Monitor — CO₂ build-up profile · CO₂ on → lights on
11:00 CO₂ on Target reached
The complete toolkit

Five tools. One dashboard. Zero compromises.

Every feature is grounded in real aquatic chemistry — not guesswork. Whether you're running a high-tech CO₂ system or working around aquasoil, AquaCalc has you covered.

📊
Real-time CO₂ monitoring
Log your pH every 30 minutes across a session. AquaCalc calculates exact CO₂ concentration at each reading and shows your build-up curve from CO₂-on to lights-on, so you can see exactly when you hit your target.
🌱
Two calculation modes
Use the precise KH/pH/temperature formula for standard tanks, or switch to the pH drop method for aquasoil and buffering substrates where the KH formula breaks down. Both modes estimate CO₂ ppm.
💧
RO water mixer
Build your tap water chemistry profile, set your vessel size and RO/DI TDS, then drag a slider to experiment with different mixing ratios. Mixed TDS syncs automatically to your pH monitor.
🎯
Standard & EI range charts
Every mixed parameter is plotted against both standard planted tank ranges and Estimative Index dosing ranges. Toggle between modes to see exactly where your water sits — per parameter, not as a crowded single chart.
⚠️
Safety alerts built in
Automatic warnings fire when CO₂ approaches your target, exceeds it, or crosses the 40 ppm danger threshold — with colour-coded row highlights and a full-width banner so you can't miss it.
👤
Named profiles, auto-saved
Create profiles for each tank — "Main 230L display", "Shrimp nano", "Aquasoil scape". Your settings, log time, chemistry list and RO ratios all save automatically per profile in your browser.
🧪
Fertiliser dosing calculator
Enter your current and target ppm for any parameter and choose your fertiliser. AquaCalc tells you exactly how much to dose — per session and per week — across EI, PPS-Pro and lean dosing methods, with a full weekly schedule.
💧
Water change calculator
Tell AquaCalc your current and target level for any parameter and it calculates the exact water change percentage and volume needed. Uses your RO Mixer values as the replacement water chemistry, and shows a multi-change breakdown.
🪣
Tank volume calculator
Calculate the exact water volume for any tank shape — rectangle, bowfront, hexagon, corner, cylinder or sphere. Adjust for fill level and substrate depth. Outputs in litres, US gallons and UK gallons.
🟢
CO₂ cylinder runtime estimator
Enter your remaining CO₂ weight, bubble rate and daily injection hours. AquaCalc estimates how many days remain, your run-out date and when to reorder — so you're never caught out overnight.
🎨
Drop checker colour guide
Enter your reference solution KH and see the exact colour your drop checker should show at every CO₂ level — personalised to your water chemistry, not a generic chart.
Simple to use

Set up in minutes, use it every day

No sign-up. No app to install. Create a profile, enter your tank parameters once, and every tool is ready to use — from CO₂ logging to water change planning.

1
Create a profile
Name your tank and enter your water parameters — KH, tank volume, filter turnover, and your start pH measured the morning after CO₂ has been off all night.
2
Set lights-on target
Generate your reading log, set your CO₂-on time, and mark which slot is your lights-on target. AquaCalc calculates your target pH from your KH and target CO₂ ppm.
3
Log readings every 30 mins
As CO₂ builds through the morning, enter each pH reading. Watch the progress bar climb toward 100% and the chart fill out — you'll see your CO₂ curve in real time.
4
Dial in your water mix
Switch to the RO Mixer tab to fine-tune your water change chemistry. Add your tap water parameters, experiment with mixing ratios, and check every value against the range charts.
CO₂ monitoring

Accurate CO₂ tracking for any substrate

Different substrates and setups need different approaches. AquaCalc covers both with a single toggle.

Standard tanks
CO₂ / KH / pH formula
The gold-standard method for tanks with stable, uninfluenced water chemistry. Uses your KH, water temperature and pH to calculate dissolved CO₂ precisely — no guesswork.
  • Exact CO₂ ppm from KH × 12.839 / 10^(pH − 6.35)
  • Target pH derived from your KH and CO₂ target
  • Degassed pH cross-check (target = degassed − 1.0)
  • Best for inert substrate tanks with measurable KH
Aquasoil & buffering media
pH drop method
When aquasoil or other buffering substrates alter your water's KH, the standard formula breaks down. The pH drop method uses your overnight pH as the true degassed baseline instead.
  • CO₂ estimated as 3 × 10^(overnight pH − current pH)
  • Overnight pH = natural degassed baseline for buffered tanks
  • Target = overnight pH minus your desired drop
  • Degassed sample field hidden — it's not meaningful here
RO water mixer

Build the perfect water for your tank

Building the right water for your fish and plants starts with knowing exactly what's in it after mixing. AquaCalc makes that instant.

Add your tap water chemistry from your water supplier's report or your own test kit. Set your vessel size, your tap TDS and your RO/DI TDS, then drag the slider.

Every parameter updates live as you adjust the ratio — so you can find the exact mix that puts all your values inside the target range before you even fill the bucket.

  • Supports any parameter — macro, micro, or custom
  • Searchable dropdown with 25+ known parameters
  • Separate mini-charts per parameter, easy to read
  • Standard and EI dosing range toggle
  • Mixed TDS syncs automatically to pH Monitor tab
  • Saves per profile — different tanks, different tap reports
💧 Live mixing — 300L vessel
Tap water 60%RO/DI 40%
180 L tap120 L RO/DI
Mixed water chemistry
Nitrate (NO3)7.8 ppm✓ Good
Calcium (Ca)32.4 ppm✓ Good
Magnesium (Mg)3.8 ppmLow
Carbonate (KH)4.2 dKH✓ Good
Iron (Fe)0.002 ppmLow
TDS138 ppm✓ Good
Built-in safety

Real-time alerts protect your fish

CO₂ above 40 ppm is harmful to fish. AquaCalc makes sure you always know where you stand, with colour-coded row highlights and prominent banners that fire automatically.

📈
CO₂ rising — 14.2 ppm
Building toward your 30 ppm target. Progress: 47%. Keep monitoring every 30 minutes.
⚠️
CO₂ above target — 34.1 ppm
Dissolved CO₂ has exceeded your target of 30 ppm. Consider reducing injection to avoid overshoot.
🚨
DANGER — CO₂ exceeds 40 ppm!
This level is harmful to fish. Reduce or turn off CO₂ immediately and increase surface agitation.
✅
At target — 29.8 ppm
CO₂ is within 5% of your target. Lights on — enjoy the photoperiod.
🔒
Runs entirely in your browser
Your tank data, pH readings and chemistry profiles never leave your device. All calculations happen on our server — your data stays in your browser's local storage.
👤
No account, no sign-up
Just open the dashboard and create a named profile for your tank. Everything saves automatically. No email address, no password, no subscription required.
📱
Works on any device
Fully responsive — use it on your phone next to the tank, your tablet in the fishroom, or your desktop when planning. The dashboard adapts to any screen size.
Free calculators

The tools every planted tank keeper needs

Beyond the dashboard, AquaCalc includes a suite of standalone calculators to help you set up, plan and maintain your tank.

Volume & CO₂
Tank volume & cylinder runtime
Know exactly how much water is in your tank and how long your CO₂ will last — two numbers every planted tank keeper needs, instantly calculated.
  • Supports rectangle, bowfront, hexagon, corner, cylinder and sphere tanks
  • Fill level slider and substrate depth adjustment
  • Outputs in litres, US gallons and UK gallons
  • CO₂ runtime from bubble rate, hours per day and diffuser efficiency
  • Run-out date and reorder reminder with 7-day safety buffer
  • Warning alert when less than 14 days remain
Drop checker
Personalised drop checker colour reference
Stop guessing what your drop checker colour means. Enter your reference solution KH and get an exact colour guide — calibrated to your specific water chemistry.
  • Shows colour, CO₂ ppm and checker pH at every level
  • Covers very low (5 ppm) through toxic (50+ ppm) ranges
  • Adjustable for 2, 3, 4, 5 and 6 dKH reference solutions
  • Explains why the standard 4 dKH reference gives consistent results
  • Use alongside real-time pH monitoring for the most accurate picture
Open the tools page →
Dosing & water change calculator

Stop guessing. Start dosing with precision.

Knowing your water chemistry is only half the battle. AquaCalc tells you exactly what to dose and exactly what water change to perform to hit your targets.

Fertiliser dosing
Precise doses across EI, PPS-Pro & lean methods
Choose your target ppm, select your fertiliser or dry salt from a comprehensive database, and get an exact dose — with a full weekly schedule tailored to your chosen method.
  • Supports liquid ferts (Seachem range) and dry salts (KNO3, KH2PO4, K2SO4, MgSO4, CaCl2, CaSO4, CSM+B)
  • EI: 3× weekly dose + 50% water change reset schedule
  • PPS-Pro: daily micro-dose matched to plant consumption
  • Lean: once-weekly minimal dose for low-tech tanks
  • Custom fertilisers — add your own concentration and element fraction
  • Tank volume synced automatically from pH Monitor tab
Water change calculator
Exact volume and percentage to hit your target
Whether you need to reduce nitrate before a water change or adjust KH with a different water source, AquaCalc calculates the precise change needed — using your actual RO Mixer values as the replacement water chemistry.
  • Works for any parameter — NO3, PO4, KH, GH, TDS, Ca, Mg and more
  • Uses your RO Mixer mixed values as the replacement water source
  • Returns exact percentage and litres for a single change
  • Multi-change table: 25%, 30% or 50% changes to reach target
  • Flags when a reduction isn’t possible with your water source
  • Directs you to the dosing calculator when raising is needed instead
💡 The complete loop
You know your tap water chemistry from the RO Mixer. You know your tank volume from the pH Monitor. So AquaCalc can tell you exactly what to dose with the fertiliser calculator, and exactly what water change to perform with the water change calculator — all feeding off the same profile. No more manual maths. No more guesswork.
Free forever · No account needed

Your complete planted tank toolkit awaits

Monitor CO₂, mix your water, dose fertilisers and plan water changes — all from one free dashboard, with your settings saved per tank profile.

Open the free dashboard →