Calcium Hardness

[chem geek]

Sorry I didn't read your post thoroughly the first time -- you had said you had an SWG and I missed that. As for knowing if the calcium is coming from your plaster, the way to know that is to calculate the saturation index for your pool so to do that we need to know the pH, TA, CYA, CH, and water temperature. However, unless your TA and pH are very low, I would be surprised if your water is that corrosive.

For example, with your CH of 200 then if your pH were 7.2 and your TA were 80 and your CYA 70 and temp 80F, then your saturation index would be -0.8 and would probably be corrosive. However, with an SWG it's hard to keep the pH low and in fact you mentioned a frequent battle of rising pH so that implies you probably don't get it much below 7.5 or so anyway.

It's possible that with your frequent acid additions you've gotten the TA so low as to be a problem or that locally acidic conditions dissolved some plaster where you poured it, but why don't you give us the full set of numbers and we can go from there.

The CH level of 550 is nothing to be concerned about, especially if you keep your TA lower to prevent the pH from rising as quickly. By the way, if there WAS corrosion, then this would make the pH and TA rise (whereas outgassing of carbon dioxide makes the pH rise without any change in TA). As for tell-tale signs, it is possible for the plaster to feel more rough and less smooth IF the corrosion were somewhat uneven, but that's speculation on my part.

Richard