Using both HEDP and Phosphate remover

[macman]

I routinely use a phosphate remover to remove phosphates from my pool water (plaster pool). I live in a warm climate and so in the summer time sometimes the FC level can get below the FC/CYA ratio. Keeping phosphates out of the water seems to be a good thing in preventing algae, but I've had issues with metal staining in my swimming pool as of recently. Iron levels are high according to the pool shop and I need to add an HEDP-containing (which contains phosphates) sequesterant.

I have read that over time this HEDP-containing product will break down and release orthophosphates into the water.

If I add my lanthanum-containing phosphate remover to my filter media before adding HEDP to the water, will it interfere with the efficacy of the HEDP in removing the mild metal stains from the pool surface that I seem to have? From what I've read phosphate removers remove orthophosphates from the water (which algae feeds on) but I'm not sure if they may also remove phosphates occurring in HEDP thus negating the effect of HEDP.

 

[Texas Splash]

@JoyfulNoise can you help please?

 

[JoyfulNoise]

Sequestering agents are phosPHONATES. These are organic molecules that contain phosphate groups in their structure. Only when chlorine oxidizes the organic molecule will it release the phosphate group as orthophosphate.

However, you should not add metal sequestering agents and phosphate removers at the same time. In fact, it is waste of time and money to do both. Your going to have to figure out what’s more important to you, stain removal or phosphate removal. You can lower your phosphates once and then switch over to mineral/metal sequestering but doing both concurrently will be pointless.

 

[macman]

Only when chlorine oxidizes the organic molecule will it release the phosphate group as orthophosphate.

However, you should not add metal sequestering agents and phosphate removers at the same time.

Does that mean though that the phosphate remover will remove both the orthophosphates and phosphonates?

I had thought that phosphate removers didn't bind to phosphonates. By using both at the same time it might allow the phosphonates to do their job and once they are oxidised into orthophosphate and no longer useful these orthophosphates would soon get bound to the phosphate remover so they can no longer feed algae.

 

[JoyfulNoise]

The phosphonates can form complexes (chelate) with the lanthanum reducing it’s effective concentration for scavenging phosphates. You should not use both at the same time.

Unless your source water has a lot of orthophosphate in it, phosphate levels don’t rise dramatically on their own. There are few situations where the constant dosing of phosphate removers is necessary. Most residential pools can dose once or twice per season and that’s all that is necessary. There is no benefit to the constant use of phosphate removers.