You probably don't need to worry about phosphates.

Pool chemical companies love selling you phosphate test kits and removers, but for most pools, phosphates aren’t the problem. If your water is clear and your chlorine is holding, ignore them. If you’re fighting persistent algae despite good chlorine levels, then test.

Phosphates are food for algae, but they don’t cause algae by themselves. Algae needs phosphates, nitrate, sunlight, and a drop in chlorine. If you keep your free chlorine at proper levels (1-3 ppm, or higher for salt/UV pools), algae can’t grow regardless of phosphates.

If you do have algae that won’t die, test for phosphates. If they’re above 500-1000 ppb, use a phosphate remover (liquid or granular). Follow the label, run the pump, clean the filter after. The remover binds phosphates so they can be filtered out.

But honestly? Most algae problems are from low chlorine, bad circulation, or a dirty filter. Fix those first before buying another bottle.