Built by hobbyists, for hobbyists
AquaCalc started as a personal project — a set of tools we actually wanted to use ourselves. It grew from there. Everything here is free, open to anyone, and built on a genuine love for planted tanks, fish keeping, and the community around them.
There is a moment every planted tank keeper knows: you have just switched your CO₂ on, your lights are off, and for the next two hours the tank is quietly doing its thing. The needle valve is set, the diffuser is spinning out a steady chain of microbubbles, and somewhere in the back of your mind you are doing mental arithmetic — is my pH dropping fast enough? Am I going to hit 30 ppm before lights-on?
That mental arithmetic is what AquaCalc exists to replace. Not because the maths is difficult, but because you should be watching the tank, not staring at a spreadsheet.
A hobby that rewards obsession
Planted aquariums sit at an unusual intersection. On one side is pure aesthetics — the art of aquascaping, the sweep of a Dutch street, the negative space of an iwagumi, the chaos of a blackwater biotope. On the other side is hard science: carbonate chemistry, CO₂ solubility curves, nitrogen cycling, the relationship between light intensity, CO₂ concentration and plant growth rate.
Most hobbyists come for the aesthetics and stay because the science turns out to be genuinely fascinating. Understanding why your KH matters, or what is actually happening in your filter media, or why aquasoil tanks behave differently from hard tap water tanks — these are rabbit holes that reward curiosity. AquaCalc grew out of that curiosity.
"The best tools are the ones that get out of the way. You should be looking at your tank, not your calculator."
The first version was a single-purpose CO₂ calculator: enter your KH and pH, get a ppm reading. Useful, but limited. Over time, as the tanks in front of us grew more complex and the questions got harder — how much substrate do I actually need? what does my water report mean in practice? is my filter handling the fish load? — more tools got added. The dashboard that exists today is the result of that process: thirteen tools, all connected through a single tank profile, all free.
Great tools should be free
This is the one principle that has never changed. Planted aquariums are already an expensive hobby — quality substrate, pressurised CO₂, good lighting, decent test kits. The last thing anyone needs is a paywall on a pH calculator.
AquaCalc requires no account, no subscription and no email address. There are no ads. Your data — your tank parameters, your pH readings, your water chemistry profiles — lives in your browser and on our server under a randomly generated anonymous ID. We cannot link it to you even if we wanted to. That is by design.
We believe the planted aquarium community is better served by open, accessible tools than by gate-kept ones. If a new hobbyist setting up their first CO₂ system can find their target pH on a free tool and dial in their needle valve correctly, that is one fewer fish killed by CO₂ overdose. That matters.
The hobby we love
Fish keeping as a whole is one of the most diverse hobbies on earth. Nano shrimp tanks. African cichlid biotopes. Blackwater rivers replicated in living rooms. Dutch aquascapes that take years to mature. Brackish estuaries. Goldfish ponds. Every one of these has its own community, its own body of knowledge, its own arguments about the right way to do things.
Planted aquariums, and specifically high-tech planted tanks with CO₂ injection, are a particular corner of that world that we find endlessly interesting. The combination of plant biology, water chemistry, aquascaping aesthetics and livestock care means there is always something to learn, something to tweak, something to improve. No two sessions are the same. No two tanks are the same.
We are all still learning
One of the things we love most about this hobby is that expertise is accessible. The person who has been keeping planted tanks for twenty years is usually happy to spend an hour helping a beginner understand why their plants are melting. The forum threads that shaped how we think about CO₂ monitoring were written by people who had no obligation to share what they knew — they just did, because that is what the community does.
AquaCalc is built in that spirit. The tools here exist because other people shared their knowledge freely — through forum posts, through open research, through decades of collective experimentation. We are returning that knowledge in a different form: practical, immediately useful, and permanently free.
If something is wrong, incomplete or missing, we want to know. The feedback page is genuinely read. If you have a tool idea, a correction to something we have written, or just a better way of explaining something — tell us. The best version of AquaCalc is the one that reflects the community's actual needs, not our assumptions about what those needs are.
What is next
The current toolkit covers CO₂ monitoring, RO water mixing, fertiliser dosing, water changes, tank volume, substrate planning, CO₂ cylinder runtime, drop checker reference, and filter capacity. That is a lot of ground, but the hobby is wider still.
We are always looking at what people are calculating manually — on scraps of paper, in forum posts, in their heads at 6am before CO₂ turns on — and asking whether a tool could make that easier. Not every idea is worth building. But the ones that genuinely save time, reduce error, or help a new hobbyist understand their tank chemistry better? Those are worth building.
Thanks for being here. Now go look at your tank.