Question for the chemists

[chem geek]

Both chlorine and MPS are selective oxidizers. That means they don't oxidize everything and they are somewhat different in what they oxidize and how long it takes. It is an oversimplification to say that one oxidizes inorganics while the other oxidizes organics.

When it comes to inorganics, this is really ammonia in sweat and urine. Both chlorine and MPS will oxidize ammonia mostly to nitrogen gas, but according to this paper, MPS reacts slowly with ammonia and instead in the presence of chloride salt its sulfate radicals forms chlorine that then oxidizes the ammonia. With chlorine, about 10% of the ammonia will become nitrate (that reaction is shown in one of my posts in this link). I don't know the amount that becomes nitrate when using MPS but it is probably similar. As far as nitrates and phosphates which are nutrients for algae, that is irrelevant since one can maintain a chlorine level in a pool that prevents algae growth regardless of nutrient level. Algae is limited in growth rate by sunlight and temperature so even if you dumped fertilizer in the pool you would still be able to control algae with chlorine alone.

As for organics, neither chlorine nor MPS oxidize urea quickly though chlorine in an outdoor pool breaks down from the UV in sunlight to produce hydroxyl free radicals that may keep urea in check. Chlorine's primary reaction with organics is that of substitution on some nitrogen sites producing Combined Chlorine (CC). MPS does not directly produce combined chlorine and will often oxidize compounds that would otherwise form CC. That is the main advantage of using MPS -- that it does not form chlorinated disinfection by-products.

The copper ions in Nature2 can prevent algae growth and kill existing algae if the concentration is high enough, but that concentration of copper ions is high enough to create stains and to turn blond hair green unless you keep the pH rather low (7.4 or lower at ALL times). If copper ions didn't have these side effects, then they would be a great product, but you can't hope or wish for the perfect product if in reality it does not exist. Chlorine is about as close as one gets since it is both a disinfectant and an oxidizer and with Cyanuric Acid (CYA) can be at very low active levels while still being effective.

The combination of Nature2 and MPS in spas, where the Nature2 in this case is silver and zinc ions, IS a reasonable alternative disinfection system that actually passes EPA DIS/TSS-12, but ONLY for spas since it requires hot spa temperatures to be able to kill bacteria quickly enough. Even so, most people find that they still need to use chlorine once every week or two to keep the water clear. However, for pools, as Ben wrote, Nature2 with MPS doesn't work well and is an expensive waste of money.