Pool test strip photo dosing calculator

The idea

Reading a test strip against the bottle chart is guesswork, and the follow-up maths (parts per million to fluid ounces of a specific product for a specific gallonage) is where pool owners give up and pour in a glug of chlorine. Over-dosing wastes money and then requires more chemicals to correct, a loop the chemical brands do not mind at all.

Clorox proved people will scan strips with a phone, but their app only recommends Clorox products. The wedge is brand-agnostic: read any strip via a vision model, then output doses in the user’s actual products, including plain liquid chlorine and muriatic acid that big-box apps pretend do not exist.

Who pays

The buyer is a residential pool owner already spending 50 to 100 dollars a month on chemicals; 5 dollars a month during swim season is a rounding error against one avoided algae bloom. Sell it as a pausable seasonal subscription through Stripe. Distribution: r/pools and r/swimmingpools, Trouble Free Pool forums, and SEO on how much chlorine to add queries, which have huge seasonal volume.

MVP scope

• Pool setup with volume calculator and owned-products list
• Strip photo scan via Claude vision, with per-pad confidence and retake prompts
• Dose card in the user’s actual products, correct order and wait times
• Re-test reminder notification 6 hours after dosing
• History chart of readings over the season
• Skip for v1: liquid drop-kit support, saltwater generator maths, hot tubs, chemical shopping links

Build StripSnap, a React Native (Expo) app that turns a photo of any pool test strip into exact dosing instructions.

Onboarding: user enters pool volume (or computes it from shape and dimensions), surface type, and picks the products they actually own from a list: liquid chlorine with percentage, cal-hypo, dichlor, muriatic acid, soda ash, baking soda, cyanuric acid. Also let them pick their strip brand from the top six, each with a stored reference chart.

Core flow: user photographs the wet strip next to the bottle's colour chart. Send the image to the Claude API with a prompt that identifies each pad, matches it against the reference chart for that brand, and returns structured JSON: free chlorine, pH, total alkalinity, CYA, hardness, each with a confidence score. Show low-confidence pads as ranges and ask for a retake if lighting is bad.

Then compute doses locally with standard pool chemistry formulas, output as a card: what to add, how much in both metric and US units, in which order, with wait times between additions. Schedule a re-test push notification for 6 hours later.

Screens: Home (latest water status), Scan, Dose Card, History chart, Settings.

Pricing via Stripe: free gives 3 scans per month; Pro at 5 dollars per month (pausable off-season) is unlimited scans plus history. Store everything locally with cloud backup optional.