CO2 Calculator: Planted Tank

Most CO2 charts hand you one confident number. That number is wrong more often than the hobby admits.

This calculator does two things differently. It always returns a range instead of a bare value, and it locks the calculation when your water chemistry breaks the method it relies on.

WHY A RANGE INSTEAD OF A NUMBER
Nobody in this hobby measures dissolved CO2 directly. It is inferred from carbonate hardness, pH and temperature, and every one of those inputs carries error. A pH reading off by 0.1 shifts the result by about 26 percent. A KH kit that resolves only whole degrees can sit half a degree off at 3 dKH, worth another 17 percent. The app carries the resolution of your actual test through the equation and reports "22 to 31 ppm" instead of "26 ppm". The band is the honest answer. A single value claims a precision your test kit never had.

WHEN THE APP REFUSES TO ANSWER
The KH/pH method assumes carbonate is the only thing buffering your water. Peat, aquasoil, phosphate buffers and many pH-down products break that assumption: they hold pH down without contributing to KH, and the formula reads that as dissolved CO2 that is not in the tank. In documented soil setups the classic table runs high by a factor of 12 to 19. So the app asks what is in your tank first, locks the KH/pH result when the preconditions fail, and sends you to the drop checker or a delta-pH run instead. A locked screen helps you more than a confident 90 ppm on a tank actually sitting near 5 ppm.

THE DELTA-pH METHOD, NOW GUIDED
Drive the CO2 out of a water sample, then measure it again. The difference between degassed pH and tank pH gives you CO2 without any KH value at all, because carbonate hardness appears on both sides of the ratio and cancels out. This is the method that still holds on aquasoil and peat, and the app now runs the step it depends on: pick an air stone or a glass left standing, start the timer, and it tells you when the sample is ready. It refuses a baseline that reads below the tank, and says so when your two readings sit closer together than your pH method can resolve.

THE PREFACTOR CORRECTION
The CO2 table copied across every forum uses a fixed prefactor. That prefactor is temperature dependent. Across the usual temperature window of a planted tank, the common table therefore reads 10 to 21 percent low. This app derives the coefficient for the temperature you actually run.

DROP CHECKER
A blue to green to yellow scale referenced to the usual 4 dKH solution, including the part most guides leave out: a drop checker lags real conditions by one to two hours. It shows where your CO2 was, not where it is.

WHAT THIS APP DOES NOT DO
- It does not measure anything. Your test kit or probe does the measuring.
- It does not replace water tests.
- It is not a fish or plant database.
- It does not calculate medication doses.

WITHOUT PAYING
All three methods, the error bands, the locks, the guided degassing, the drop checker scale with its reference recipe, the tools for tank volume, hardness units and dosing, and pH sessions across the photoperiod with the curve and the drift reading. One tank, with the last 30 saved readings.

CO2SCAPE PRO, 6.99 EUR, ONE PURCHASE
- Unlimited tanks instead of one. Each tank keeps its own hardness, temperature, substrate declarations, target range and readings.
- Unlimited history instead of the last 30 readings
- Reminders at your chosen interval while a session runs
- CSV export of the readings of the tank you are viewing
Pro is a single purchase, not a subscription, and it works with Family Sharing. It extends the record keeping, not the chemistry.

NO ACCOUNT, NO CLOUD
Everything you enter stays on the device. No login, no server of ours, no sync. This version shows advertising, which Google's ad kit loads over the network, and CO2Scape Pro removes it. Apart from that the app talks only to Apple's own App Store machinery, which handles the purchase of Pro and restoring it on your other devices.