Scaling/Precipitation Questions

[tomfrh]

I have a question about calcium precipitation in our pool.

It’s a 50,000L concrete pool with a two-year-old white cement PebbleSheen interior. The system includes a saltwater chlorine generator (salt at 3500 ppm) and a cartridge filter.

Current water chemistry:
pH: 7.8 (I generally allow it to sit here; if it rises higher, I bring it down to ~7.2)
TA: 60-70
FC: 4
CC: ~0
Phosphates: ~0
CYA: 30
Calcium hardness: 350
Salt: 3500
Saturation Index: Close to zero

There are fine calcium flakes and dust collecting below the return jets — likely from the chlorinator. More significantly, there’s a much finer calcium “dust”in the pool, causing persistent cloudiness and dull water. The water lacks sparkle, and the dust clogs the cartridge filter every few weeks. When I clean the filter, most of the material is this white powder, which im fairly sure is calcium deposits.

When I add Calstop, the problem disappears. No more flakes or dust. Water becomes clear again. Filter doesn’t clog for months

Eventually, though, Calstop stops working and the issue returns. I'd prefer a long-term fix without relying on chemical additives.

What’s driving the precipitation despite balanced water and an LSI near zero?

Is there a solution aside from calstop? Should I run the scaling index more negative?

Appreciate any insights.

 

[bigpoppapoolman]

Likely formed when the water ph and calcium and alkalinity was previously very high. It can create the scale inside the salt cell and pool plumbing. The precipitation and forming of that increase when the water warms up. Overtime it will go away if the water is kept in acceptable ranges or just slightly on the acidic side (TA 50-70 and ph 7-7.2 , CH less than 200). It’s a mess when the flakes come out as the water warms … but now you know and you’ll keep it in range from here out. It’s pretty common for new gunite pools with salt systems do this … it’s that time when the builder is turning over the pool water responsibly to a new to pool life person that just can’t believe that they need to add even more muriatic acid to keep the water balanced. So they loose control of it … all the while it’s become very alkaline and the water temp is going up accelerating the build up inside the plumbing and want cell. Sometimes if the flakes just sit on the plaster for days … they can stick and have to be removed with a plastic scraper.

 

[Bperry]

I have a question about calcium precipitation in our pool.

It’s a 50,000L concrete pool with a two-year-old white cement PebbleSheen interior. The system includes a saltwater chlorine generator (salt at 3500 ppm) and a cartridge filter.

Current water chemistry:
pH: 7.8 (I generally allow it to sit here; if it rises higher, I bring it down to ~7.2)
TA: 60-70
FC: 4
CC: ~0
Phosphates: ~0
CYA: 30
Calcium hardness: 350
Salt: 3500
Saturation Index: Close to zero

There are fine calcium flakes and dust collecting below the return jets — likely from the chlorinator. More significantly, there’s a much finer calcium “dust”in the pool, causing persistent cloudiness and dull water. The water lacks sparkle, and the dust clogs the cartridge filter every few weeks. When I clean the filter, most of the material is this white powder, which im fairly sure is calcium deposits.

When I add Calstop, the problem disappears. No more flakes or dust. Water becomes clear again. Filter doesn’t clog for months

Eventually, though, Calstop stops working and the issue returns. I'd prefer a long-term fix without relying on chemical additives.

What’s driving the precipitation despite balanced water and an LSI near zero?

Is there a solution aside from calstop? Should I run the scaling index more negative?

Appreciate any insights.

Can you post the actual test results? “Near zero” isn’t close enough to judge. If you have some long term data to look through, that would help as well. Generally speaking we recommend keeping the CSI slightly less than zero to avoid scaling and also note that CSI and LSI aren’t the same thing.

 

[JoyfulNoise]

You can run the pool in the negative CSI range for a while and see if it helps. Just remember that inside the SWG cell that the pH is a lot higher than bulk pool water. So if your CSI is zero in the pool, your CSI inside the cell when it is generating can be extremely positive and well into the scaling range.