Magic White Dust

[Rachel&Blake]

Howdy! We are new pool owners and this is our first summer with a pool. Earlier this spring Pool Math Calculator showed calcium hardness was too low. I added calcium carbonate early summer as suggested. Salt level has been high this summer. I have been adding water to top-off, and replacing water from top of skimmer level to bottom of weir level to try to lower.

As the water warmed during early summer, I started to notice saltier water and gritty white substance almost looking like undissolved salt on bottom of pool near return jets. The grit is mostly collected in the hayward pool robot cleaner, and I need to vacuum it up from the swim spa and areas the robot cannot reach. After vacuuming I clean our hayward swim clear cartridge filter with a water hose jet as our installer instructed. Typically the next day, the gritty white substance is back, collecting on flat surfaces near the return jets.

When the water was cold over the winter and spring, the CH was low and the salt was on the low end of normal, we did not have this issue; however I am not sure if there is a relationship. Any suggestions on how to mitigate the white gritty substance?

Pool was installed in December 2021 and I vacuum and clean cartridge filter regularly, weekly since late May. Our pool is approximately 9K gal, fiberglass in ground pool. Hayward Swim Clear filter, Hayward SWG. Water temp has been running 88-92', and we are running a chiller to cool 85'. Salt is 3600-3700 per Taylor test kit, though SWG is reading closer to 3400.

 

[Texas Splash]

Welcome to TFP! I suspect the first place we should start with your scenario is a full set of water test results from either a TF-100 or Taylor K-2006C. Do you have one of those? Pool Care Basics

 

[Rachel&Blake]

Welcome to TFP! I suspect the first place we should start with your scenario is a full set of water test results from either a TF-100 or Taylor K-2006C. Do you have one of those? Pool Care Basics

Howdy! Thank you for writing back! I have a Taylor K2006, and a Taylor Sodium Chloride kit. Here are the test results from 18:50H this evening-
FC 3.0
CC 0.0
pH 8.4 (estimated since scale ends at 8.0)
TA 250
CH 200
CYA 55
SALT 3600
TEMP 88F
CS! 1.01
Air TEMP 98F
Notes:
Using Pool Math App to calculate interventions.
CYA trending down since adding 5# dry stabilizer in March. (320 on 3/20/22)
CH trending down since adding about 760 oz over May and June. (230 on 6/5/22)
pH continually rebounds back to >8 within a day or two of adding muriatic acid.
TA trending constant 200-250.

 

[jedigrover]

That high TA & pH is driving the scale production. Your CSI > 1 is very much on the scale-producing side of the equation. That's what's driving this gritty white substance. That is calcium scale.

 

[Texas Splash]

I'm on board with Jedi. ^^ Once you get a consistent handle on the pH, it should eventually settle down. As a test, I suppose you could collect some of that white stuff, place it in a pile, and pour some vinegar or acid on it to see if it fizzles. I expect it would.

 

[jedigrover]

I imagine the CH trending down even after adding calcium is due to it falling out of solution as scale.
The pH rising so much is due to the TA being so high.
You are going to have to use a great deal of acid to work that TA down.
You might consider a partial water swap to help. But test your fill water first. If your TA is that high, I suspect you might have high TA fill water.

Check your SWG. It is likely that it is getting quite scaled up.

 

[Rachel&Blake]

Thank you for this information. I am reading in Pool School that I should manage the interventions using the Pool Math app and this will bring the CSI within range. My target pH has been 7.2 and I am adding about 2 quarts of 31.45% 20' Baume muriatic acid about once a week, after testing (which always reads >8.0, even if not adding any water between tests). I understand controlling pH and thus TA is the key to helping with CSI. What frequency should I be testing the water and adding muriatic acid, as weekly does not seem to be sufficient?

 

[Texas Splash]

What frequency should I be testing the water and adding muriatic acid, as weekly does not seem to be sufficient?

Short answer ... however often it takes. It will fluctuate. Right now with an elevated TA, your pH will want to pop-up a little quicker. So once the pH hits 8.0, knock it down to 7.2 and that will bring the TA down a notch each time you do it. After several repeated efforts like this, the TA will eventually get down to the 60 - 80 range or so which should really help stabilize your pH much better.

 

[Rachel&Blake]

Short answer ... however often it takes. It will fluctuate. Right now with an elevated TA, your pH will want to pop-up a little quicker. So once the pH hits 8.0, knock it down to 7.2 and that will bring the TA down a notch each time you do it. After several repeated efforts like this, the TA will eventually get down to the 60 - 80 range or so which should really help stabilize your pH much better.

Copy that! I'll work on adjusting for CH and CYA as well. Thank you for your help!

 

[jedigrover]

I would not adjust CH until after you get the TA and pH down enough to result in a CSI <= 0.3.

Right now, with the conditions of your water, it is saturated with calcium, which is why it is precipitating out of solution.