White crystals in robot basket.

[Kellyp]

I should have taken a pic, but didn't think to at the time. It looks sort of like dried salt, but my salt is not high, or recently added. I can't think what it might be. My calcium is always low, fill water only has 20 ppm, it has already dropped from my calcium add earlier this spring.

Can anyone guess from my pool math logs or should i vacuum again and try to get a pic?

I did not try putting muriatic acid on it, I am already nervous putting it in the pool despite having lots of experience doing just that, but I can if it will help figure out what it is.

TIA

 

[ajw22]

Could be scale ejected from your SWG.

Reducing your TA can help prevent scale from forming in the cell.

From TA - Further Reading

Why Should TA be Lowered with a SWG?[edit]​

Usually a TA on the high end is fine if the pH is stable. However TA does need to be adjusted down with an SWG. The problem is, INSIDE the cell, the CSI is very different than in bulk pool water.

With high TA and aeration from the bubbles the SWG creates, you'll get faster pH rise inside the cell and so there's more potential for scaling. With current reversal, the cell tends to stay clean but you'll get more snowflakes out of the returns. Calcium hardness is only one part of the equation.

If the SWG cell pH rises much above 10 (and it can easily do that) and if there is sufficient levels of carbonate ions available (CO3--), then you will get calcium carbonate precipitation. The higher the TA and pH, the more carbonate anions are available.

Borates are particularly helpful preventing scale in a SWG because the pKa for boric acid / borate anion buffering is approximately 9. That essentially means you get the maximum buffering capacity at a pH of 9 and that tends to hold down the pH rise inside the cell. Keeping the pH below 10 in the SWG cell reduces the risk of calcium and magnesium scaling (insoluble magnesium hydroxide precipitates at a pH of 10.2 or so).

 

[Kellyp]

Thanks, I did raise alkalinity for over winter to keep my csi in line. My fill water, is low, around 50, so I was just going to let it drop naturally, but I'll acid and aerate instead.

Appreciate your input.