Am I reading this right? Natural Chemistry Metal Free.

[rcy]

First of all, the MSDS for this product shows Citric Acid, CAS # 77-92-9, 0.5 - 1.5 %. I know Citric Acid is a stain remover, but does it also bond to metals, or is this a mistake in the MSDS?

Secondly, in the FAQ section it states -

"It is important to use a non-polymer filter aid with sand and cartridge filters while removing metals because metal particles are so extremely tiny that they can slip through the sand and cartridges and return to your pool water. The use of a filter aid traps the metal particles until the filter is backwashed or cleaned out."

So, if I'm understanding the literature, this product will either bond to metal, or release it from the surface it's staining, and then the metal will be trapped in the filter (in the case of sand or cartridge, if you use a "non-polymer filter aid") and then can be backwashed (DE or sand) or cleaned (cartridge) from the filter.

Doesn't this mean that the metal will be permanently removed from the water? I thought this couldn't be done (CUlator maybe, maybe not), and that the metal could only be bonded to something, but would still be in the water?

 

[chem geek]

Citric acid is a metal chelator (sequestrant), but in the presence of chlorine citric acid gets oxidized and produces trihalomethanes (THMs), especially chloroform. Natural Chemistry sells phosphate removers so all of their metal sequestrants are phosphate-free, but that means most of them aren't as strong metal sequestrants or they are more susceptible to oxidation by chlorine so create a higher chlorine demand. HEDP-based metal sequestrants are better as they are more chlorine-resistant and are strong in binding to metals.

As for their statement regarding removing metals, that is referring to metal oxides which are solids that can get caught in the filter. The presumption here is that there are so many metals in the water that some have formed oxides. The metal sequestrant is to capture free metal ions to prevent them from forming more oxides if the pH were to rise, for example. These metal sequestrants, even when bound with metals, will not generally get caught in the filter as they are not generally solid.

 

[rcy]

That explains why the instructions state to add x amount per week after the initial treatment (because it's being oxidated by the chlorine).