Phosphates are one of those pool topics that comes up constantly at pool stores and almost never comes up among experienced DIY pool owners. There’s a reason for that gap, and it’s worth understanding before you spend money on a phosphate remover.
What Are Phosphates?
Phosphates are compounds containing phosphorus. They get into your pool from a lot of different sources: dead leaves and organic debris decomposing in the water, fertilizer runoff if you have landscaping nearby, certain pool chemicals (some algaecides and sequestering agents contain phosphate compounds), fill water, and even swimmer waste like sweat and sunscreen.
The reason people care about them is that phosphates are a primary nutrient for algae. Higher phosphate levels, the theory goes, give algae a better food supply and make blooms harder to kill.
What the Pool Store Will Tell You
If you bring a water sample to a pool store, there’s a decent chance they’ll test for phosphates, find them “elevated,” and recommend a phosphate remover. These are typically lanthanum-based products that bind to phosphates and cause them to precipitate out of the water so the filter can catch them. They’re not cheap – a decent phosphate remover treatment can run $20-60 depending on pool size and phosphate levels.
That doesn’t make them a scam exactly. But pool stores have a financial interest in selling you things, and this is one of the easier up-sells to make when the test number looks scary.
The Other Side of the Argument
The Trouble Free Pool community — which is probably the most knowledgeable DIY pool forum out there – takes a pretty direct position on this: phosphates don’t matter if you maintain adequate free chlorine. Their reasoning is that algae needs multiple things to grow — phosphates, CO2, sunlight, and primarily a low enough chlorine level to survive in. If chlorine is at the right level for your CYA, algae won’t get established regardless of phosphate levels.
There’s a lot of logic to this. The overwhelming majority of algae problems in pools come back to a chlorine problem – low FC, high CYA relative to FC, or an inconsistent dosing routine. Treat the chlorine, solve the algae. Phosphates are usually a red herring.
So What Should You Actually Do?
Honestly – if your pool is clear and well-maintained, don’t bother. Get your free chlorine to the right level for your CYA and keep it there. Algae won’t be a problem and you won’t need to spend money on phosphate removers.
If you’re fighting persistent algae despite correct chemistry and you’ve ruled out other causes, then a phosphate test might be worth doing as a one-time check. If phosphates are genuinely very high (over 1,000 ppb), a phosphate remover used once as part of the troubleshooting process is reasonable. But it shouldn’t be a routine ongoing product in your maintenance budget.
If You Do Want to Test
Standard test strips and 5-in-1 kits don’t measure phosphates. You need a separate phosphate test kit or you can have your pool store test for it specifically. Target is generally under 100-200 ppb, though you’ll see different numbers depending on who you ask. If your pool is running fine with correct chemistry, skip the test entirely – you have better things to spend time and money on.