Why Is My Pool Cloudy but My Spa Is Clear After Shocking?

General Forum
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I’m struggling with black algae in my pool, and last night I brushed and quad shocked both the pool and spa. As expected, both became cloudy. I ran the filter on high overnight.

This morning, the spa is crystal clear, but the pool is still cloudy. All my valves are open, and I assumed both the pool and spa, sharing the same pump and filter, should be equally foggy. Why is only the pool cloudy?

Could something be wrong with the system, or is this normal?

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  • What’s your location?
  • Shock the pool, use a brush, and apply copper 7 algaecide. If it were my pool, I’d dive in with a brush in hand—even a toothbrush works pretty well. It’s much easier than using a pool brush.
  • Ensure the filter is functioning properly. Clean or backwash it if needed. Also, have your water chemistry tested. Is your chlorine level stable?
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I’m guessing the spa looks clearer because it’s smaller and filters faster. But if your spa and pool share a pump with a spillover or waterfall, double-check that it’s not stuck in spa mode. As long as the pool returns are working or you see the spillover/waterfall running, you should be good.

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I’m new to pools, but shouldn’t you be using an algaecide along with a phosphate remover (since phosphates are algae food)? That’s what my pool builder recommends for mine on a weekly basis.

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@DiveDeepDreamer High-copper algaecides are excellent for treating black algae, provided they are double or triple chelated. However, when dealing with green or yellow algae, liquid algaecides should generally be avoided. For a more effective solution, I recommend Coral Seas Yellow Out, a non-sodium bromide algae killer that works on all types of algae.

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@CurrentCraze What about the phosphate remover in phase two? It cannot survive if it is unable to eat.

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Phosphate removers work wonders, especially when applied near filter cleanings or backwashes. They help deplete chlorine caused by the ongoing growth of microalgae spores. However, when algae die, they release phosphates. You can certainly treat the pool aggressively and add phosphate removers, but be aware that the dead black algae will release phosphates, and if you don’t perform weekly treatments, it might return.

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@CurrentCraze Every week, I perform shock, tabs, ozone, UV, metal chelant, algaecide, and PO4 remover. Everything is going OK so far. Glistening…

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@DiveDeepDreamer Fantastic, is it an aop system or ozone and UV?