Grainy substance at bottom of pool; Salt cell readings incorrect

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ShazamFlorida

New member
Jun 23, 2024
2
Central Florida
Hi All,

I have a relatively new pool (just over one year old). Gunite with a cartridge filter and salt cell. Pool had no issues until recently when two issues started - not sure if related or separate but seem related.

1. About a month ago the digital reading from the salt generator started fluctuating wildly both down and up but mostly down. Went from 3300ppm to as low as undectable. Salt cell was acid washed a few weeks ago and digital reading temporarily normalized for a few weeks but has again started to fluctuate (3500 last week to as low as 2400 yesterday now reading 2700)
2. Around the same time the salt cell reading started to fluctuate I noticed a whitish grainy (not slimy) substance at the bottom of the pool (not on the sides). If brushed it clouds suspends temporarily in the water then settles back. Water otherwise crystal clear. Feels grainy to the touch and not on the walls so doesn't seem like mustard algae.

Current levels
Chlorine 3.0
pH 7.6
Salt 3200 (actual reading not from digital display)
Stabilizer 50
Alkalinity 80
Calcium 220

Any thoughts would be appreciated.

Thanks so much!
 

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Welcome to TFP! :wave: That stuff seems a little bright to me to be dead algae , but perhaps it is. I have to say, we place very little faith in testing by anyone other than the actual pool owner using either a TF-100, TF-Pro-Series, or Taylor K-2006C test kit. That's always step #1 because it's so critical. Your FC is on the low end per our FC/CYA Levels, as is your CYA which we recommend to be 70 for a salt pool. If your cell is acting up, it's possible you've not been producing the chlorine you thought was happening and have been getting some algae in the water.

I would first recommend performing an Overnight Chlorine Loss Test, but to do that you need one of those test kits noted above.

Also visit -----> Pool Care Basics
 
Also see the article below which helps to compare kits.

www.troublefreepool.com

Swimming Pool Test Kits Compared

What pool test kit should I buy? Why shouldn't I use test strips? Our recommended test kits will pay for themselves in no time!
www.troublefreepool.com www.troublefreepool.com
 
My issues are nearly identical to yours. My pool is also only 2 years old. You determine the cause from your side? I have stonescapes pebble and the installer was basically a first time installer (found out later) and made a bunch of mistakes. I’m not sure if it’s related or not ..
 
Hi-

Dcrolltide - I think this is what's going on with my pool: As Texas Splash predicted, it seems the chemistry levels I reported (from weekly pool service company) were not correct.

I had to get a maintenance company in to address the salt cell and what they found is that the pH and alkalinity are sky high. My understanding is that when the salt cell splits the calcium chloride to create chlorine, the byproduct is calcium carbonate. When pH is normal, the calcium carbonate dissolves. When pH is high, it precipitates out as a grainy substance. This explains the stuff at the bottom of the pool.

It also explains the salt cell readings. The calcium carbonate deposits all over the salt cell so it can neither read levels correctly nor generate chlorine correctly. The cell had to be acid washed to get the calcium off. Now it's functioning properly but obviously this will recur if the pH is not corrected.

I'm taking Texas Splash's advice. I ordered one of the recommendes testing kits. I will start regularly testing as per the guidelines on this site and using the calculator app so I can take matters properly into my own hands.
 
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