Water chemistry that shows its working

Tubside is a hot tub app that tells you what to add, why, and how sure it is. It is being built now, and it is not on the App Store yet.

What it does

You test your water and type in what you read. Tubside works out what to add from the chemical you actually own, at the strength printed on that container, for the volume your tub actually holds. It learns how fast your water loses sanitiser and tells you when it will next need attention.

That last part is the reason it exists. A hot tub is small, hot, and heavily used relative to its volume, so it drifts fast and it drifts differently from anybody else's. A number that is right for a pool is often wrong here, and a number that is right for your neighbour's tub is often wrong for yours.

What it will not do

It never presents a prediction as a measurement. Anything modelled arrives with a range and the word estimated on it. Numbers you measured never do.

It will not call the water safe without evidence. Below the confidence it needs, it says to test before you get in. Being wrong in the cautious direction wastes a little chlorine; being wrong the other way puts somebody in unsanitary water.

It says when it does not know. A tub with three readings gets told the model has not started yet, rather than a decay rate invented from noise.

It will never combine two chemicals into one instruction when mixing them is dangerous. Acid and hypochlorite make chlorine gas. That is enforced on the chemical records themselves, not left to the wording of a screen.

Where the numbers come from

Published sources, cited in the code beside the constant they justify: the TroubleFreePool spa doctrine, PHTA guidance, EPA registration labels for the products themselves, and the CDC Model Aquatic Health Code. Where no source gives a number, the app says the number is a guess rather than dressing one up.

Your data stays on your phone

There is no account, no server, and no analytics. The app makes no network requests at all, and the build fails if anybody adds one. See the privacy policy for the whole of it, which is short.

Getting in touch

support@tubside.app. If a dose ever looks wrong, that is the most useful mail you can send — see support for what to include.