Amazingly enough, I was just about to start a new thread when I saw this one. My basic premise is this:

All pools need some calcium



Now my above conclusion is based on the the Langelier Saturation index. I suppose the real question is, do you believe in the SI or not? If you don't, then I essentially don't have much basis for my conclusion. If you do believe in it, then my argument may have some merit.

Now, I don't know for sure if I'm right or not, that's why I'm hoping I'll get some input on this thread. I'm sure someone will join in.

Here's the deal. With the SI, you want to keep your water "balanced". That is to say, not in a corrosive condition, and not in a scaling condition. I was answering some questions today on here, and ran a few scenarios through the SI calculator found here:

http://www.csgnetwork.com/langeliersicalc.html

Basically what I found is that if you have a normal pool, which is:

Temp 82
Alk 125
pH 7.6


You can't stay out of a corrosive condition without some calcium in your water. Now it doesn't take much to get out of that corrosive condition, 125 ppm seems to do the trick. The other interesting thing is that with the above pool example, even having sky-high calcium, doesn't put you in a severe scaling condition. It is also true that the SI can indicate a balanced condition, even when it isn't, so that result may be suspect.

Now this makes sense to me, mainly due to entropy, basically meaning that everything wants to balance out. Ca is a metal, and if you don't have metal ions in your water, the water "wants" them, and will pull them from whatever availible source. This may be the ladder in your pool, your heat exchanger in your heater or the metal parts in your pump. If you kick a bit of Ca into the water, you satisfy that need, and then the water doesn't attack metal parts.

The other interesting thing is that I think that the needed Ca level is low enough, that it is probably naturally found in the fill water used for pools.
So, it may not be a matter of needing to add Ca, you may just need to check to see if you have enough.

Comments?

Michael