Sodium Hexametaphosphate

Rancho Cost-a-Lotta

Silver Supporter
Apr 10, 2018
1,623
Rancho Cucamonga, CA
I've seen this chemical in some water softener salt and some multi-component pool sanitizing products. It appears to be some sort of clarifier or sequestrant that plays some role in calcium reduction.

I'm not planning to add it to my pool, but I'm curious what would happen if this did find it's way into a pool.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
17,379
Tucson, AZ
SHMP is used to sequester iron in water softeners so it doesn’t damage the exchange resin. If you don’t have iron in your municipal water, then it’s not necessary. It’s a waste in pool products as it will simply breakdown over time into orthophosphates.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
17,379
Tucson, AZ
It will bind to any divalent ion so it can sequester a small amount of calcium. The problem is that it works better at higher pH (above 8.2) and chlorine will break it down into orthophosphates. That can cause calcium phosphate scaling which is very difficult to remove.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
17,379
Tucson, AZ
I did see some claims as it working as a hardness reducer for home plumbing.

Thank you!
Its just a sequestering agent so it reduces the potential for calcium scaling, it doesn’t actually reduce or remove any calcium. It wouldn’t make a practical sequestering agent as you would have to use a fairly high concentration of it and that would eventually lead to eutrophication of septic and waste water systems. Phosphate based cleaners and descalers are essentially banned from residential use as they contribute to algae blooms in surface waterways.
 
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