How do phosphates get in the pool water ?

I just tested our tap water. It has about 200 ppb phosphates, so that is where a lot of it is coming from. When I first tested the pool water it was about 400 ppb. I guess the extra came from leaves. Now that I have gotten it near 0 it should be pretty easy to keep it there. I am using PhosFree.
 
Phosphate removers should be seen in the same vein as algaecides such as copper ions or Polyquat 60. It's not that it does not work to at least slow down algae growth. It's that it normally isn't necessary if the proper FC/CYA ratio is maintained, at least for green and black algae. For yellow/mustard algae, a higher FC/CYA level is needed to inhibit that algae so normally people try and completely eradicate it instead by getting into the shady places it likes to hide (light niches, under removable ladders, inside brush/net poles, etc.).

Also, some of these algaecide products have side effects -- copper can stain plaster pools, for example, and turn blond hair greenish. Phosphate removers can be expensive if there are a lot of phosphates to remove and they only remove orthophosphates, not organic phosphates, so if chlorine gets to zero one can still get algae growth if bacteria convert some organic phosphates to orthophosphate. That's why the only algaecide we recommend is Polyquat 60 (50 ppm Borates are also a mild algaecide, but we don't talk about that kind of use since it's rather mild) and even then only under unusual circumstances or when the chlorine level is known to get too low such as during the ascorbic acid metal stain removal treatment.

Tom, are you referring to your algae that seems to come back and might be yellow/mustard that you describe in the thread My battle with algae? You aren't talking about the pollen you describe in the thread Keeping water clear when there is heavy pollen, are you? It sounded like your pool has poor bottom circulation so without fixing that then some additional assistance is needed. It sounds like you experimented with copper algaecide, but did you ever try the Polyquat 60? At least that would not have potential side effects, though it does need to be added weekly.
 

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