White Powder

Can someone identify this white powder? I DO NOT have a DE filter. I have a cartridge filter. I have been vacuuming it up on and off for days. The pool is vinyl and chemistry is within specs.

Hi Chief, what chemicals are you putting in your pool (and what is your calcium level)?  Depending upon the sanitation method you use, it is probably calcium.  You can test this by putting a drop or two of your muriatic acid on it and see if it bubbles up. Using a good test kit like the Taylor K-2006 will give you very accurate readings of the calcium in your water.

Calcium gets added to pools inadvertently with cal-hypo shock and some forms of granular chlorine and chlorine tablets.  Using liquid pool chlorine (or cheap, plain, unscented, unthickened bleach) can help keep your calcium levels from increasing.  Some areas of the country (particularly the southwest) can already have very hard water (high calcium content) which only makes this worse.

The only reliable way of lowering your calcium hardness is to drain a portion of your water and refill it with fresh water. Then, test the new water’s hardness level before adding it to the pool. We don’t want to add new water with similar or higher calcium levels to your already hard water.