Phosphonic Acid - does it raise phosphate level?


LifeTime Supporter
Apr 25, 2009
Burlington, ON, Canada
Might be a dumb question, just based on the name, but if one uses a stain and scale treatment that has phosphonic acid in it, will this increase the phosphate level in the pool? I know phosphates don't matter etc. etc., I'm just curious as to where my phosphates came from. I've tested my rain and tap water and the test shows 0 for them.

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
San Rafael, CA USA
Phosphonic acid is a generic term that can refer either to the inorganic acid that will directly raise phosphate levels or to the organic acids aka phosphonates (such as HEDP) that are typically found in metal sequestrants. These latter compounds will slowly breakdown from chlorine and produce phosphates. This takes longer for HEDP which is one reason why we recommend metal sequestrants that use this compound. There are other phosphonates that break down more quickly and I experienced this myself as I described in this post.

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