White, gritty, substance?

[cap10gus]

What is the white gritty silt in my pool?

Three year old salt water in-ground pool. Pentair cartridge filter.

I am finding an increasing amount of a white, gritty substance in my pool. It has the consistency of very fine sand. I used to see small amounts at the bottom of the spa below the inflow. Then I started seeing an increasing amount in my pool cleaner"s silt bag. Then yesterday when I removed the cleaner's hose from the pool side, I saw more of this substance trapped at the hose's screen filter. Previously I hadn't seen more than a couple flakes trapped at the screen occasionally.

I cleaned the cartridge filters at the beginning of the season, SCG has only a very slight amount of calcium. Chemistry is almost always good with acid added almost weekly to balance pH. I brush every couple weeks or more.

Never had a problem with water clarity. The substance doesn't cloud the pool because it sinks.

I have had calcium deposits accumulate on the tile but not significant and easily removed once a season with plastic brush and acid.

 

[JimMarshall]

Based off those chemistry numbers, it’s likely calcium flakes precipitating out of the pool.

Pool store tests are notoriously inaccurate though.

But based on those numbers, pH is WAY HIGH. That combined with the CH number is what’s causing scaling

 

[cap10gus]

I suspected calcium too but not sure why it has only recently been occurring. The pH is usually higher when i have the water tested prior to adding acid for the week. Then it usually settles back to within normal. I use strips weekly and pool store every 2 or 3 weeks.
I will start testing more often and to watch the pH level more closely.

 

[JamesW]

Try putting a drop of acid on the grit to see if it bubbles.

What plaster do you have?

You should get your own good test kit.

 

[cap10gus]

Pebble Tec finish. I've used test kits initially but always had trouble distinguishing between the subtle color variances. That is why I use test strips and have the water tested every couple weeks.

The thing that throws me about it being calcium is that I expected to see heavy deposits on the salt cell when I inspected it which wasn't the case. It had maybe 1/2 teaspoon and I hadn't cleaned it since last fall.

Will bubbling acid confirm if it is calcium?

 

[rowiac]

Pebble Tec finish. I've used test kits initially but always had trouble distinguishing between the subtle color variances. That is why I use test strips and have the water tested every couple weeks.

The thing that throws me about it being calcium is that I expected to see heavy deposits on the salt cell when I inspected it which wasn't the case. It had maybe 1/2 teaspoon and I hadn't cleaned it since last fall.

Will bubbling acid confirm if it is calcium?

Yes.

Also strips as well as pool store tests are notoriously inaccurate. You should consider investing in a Taylor K-2006 or Tftestkits TF-100 test kit. The color change is much more obvious than with the typical--what shade of yellow is that?--type of test. You can also get an electronic pH tester if you have trouble judging the pink color of the liquid pH test.

 

[cap10gus]

Thanks for the suggestions. Calcium was confirmed when it fizzed after contact with muriatic acid. In hindsight, I may have gotten lax on adding acid weekly to balance the pH. Testing every couple days for awhile to monitor. Like I mentioned earlier, I've had the pool for 3 years and it's always been crystal clear, even after rainstorms when my neighbors' pools turned green and I never done more than add acid and adjusted the chlorinator. (and I am a fanatic about keeping the surface clean as it is something I kind of enjoy doing)

 

[mknauss]

What SWCG do you have? Can you add that to your signature?

The calcium is coming from the SWCG when the polarity reverses. It sheds calcium scale at that time.

If you want to maintain your SWCG you should learn about and monitor CSI - Calcium Saturation Index (CSI) - Trouble Free Pool. It is calculated using Poolmath by entering your test data from your own proper test kit.