Will I get more alkaline minerals out by draining from skimmer or from main drain?

Hi,

In the desert where I live the water is hard and it's necessary to drain your pool every several years. I'm at that point, as my pool just gobbles up acid with nary a swing in pH. Can't do it now though because in the summer the 100+ degree heat would damage the plaster. So I want to drain a little at a time. Maybe I can do this more efficiently if I target either the water near the top -- skimmer -- or bottom -- main drain. Would the calcium and other minerals tend to float upward (seems unlikely but that's only a guess), or to settle to the bottom?

Thanks,

Ted

Dissolved minerals are pretty much equally distributed through out the water, so it won't really matter where you drain from. It does matter how much you drain at a time. For example, if you have a 10,000 gallon pool, and you drain & replace 1,000 gallons 5x, you'll only have replaced 40% of your water, even though you've added 5,000 gallons. The reason is, on each successive partial drain, you drain part old water and part new water.

If you drain 1/3 of your water 3x, you'll replace 70% of your 'bad' water. [ (1-0.33)^3 ]

By the way, you'll be better off if you use muriatic acid instead of "pH Down" or some other form of sodium bisulfate for your acid source.