Tubside, a hot-tub chemistry app that shows its working

Field notes

The proposed workflow uses the chemical product actually on hand, its printed strength, the tub’s stated volume, and repeated water readings rather than a generic pool formula. The site says the model does not begin until three readings are available, and that uncertain decay estimates appear as ranges marked “estimated.” Source references named on the page include EPA registration labels, PHTA guidance, TroubleFreePool spa guidance, and the CDC Model Aquatic Health Code.