You probably don't need to test for phosphates.

You probably don’t. Phosphates are a food source for algae, but in a well-maintained pool with proper chlorine levels, they don’t matter. The algae-fighting industry loves to sell you phosphate removers, but it’s mostly a solution looking for a problem.

If you have stubborn algae that won’t die despite good chlorine and pH, then sure — buy a cheap test kit (dip strip or liquid) at the pool store. Follow the instructions: take a sample from elbow-deep water, add reagent, compare color. That’s it.

But before you bother, check your chlorine, pH, and cyanuric acid first. Nine times out of ten, those are the real issue. Phosphates are the scapegoat.

Focus on chlorine and pH instead.