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Blue slime


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While trying to balance the chemicals in our pool after it was shut down due an equipment failure the water turned cloudy and light blue.  We ran the filter overnight and the filters were clogged with a cyan blue slime.  The pool was clear before the incident.  Ph was low, below 6.8.  Free chlorine was not registering but total chlorine was high.  I added Ph up using the recommended dosing.  Later the same morning, we added a small dose of shock and that seemed to initiate the problem.  Any ideas what happened?





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pH was below 6.8 but you don't know just HOW low. My guess is that your water was VERY acidic

You don't give any test results so I really can't comment but I have seen this before when the pH was dangerously low. I noticed the endcaps of your filter are blue. Are they by any chance gummy feeling or slimy feeling? I have seen very low pH 'dissolve' filter endcaps and other parts and I suspect that is what happened.  It often occurs when someone puts trichlor tabs, which are extremely acidic, in the skimmer basket, or even more dangerous, into the pump strainer basket. However, without knowing the actual water parameter when it happened it's impossible to really know what happened in your pool but it sure seems like very low pH caused something blue to dissolve.


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  • 4 months later...
On 8/27/2021 at 8:38 AM, Jeffrey W. said:

I have experienced the exact same problem and can confirm that my pool pH was NOT dangerously low.  I check daily and it is generally around 6.8 or slightly higher. I wish I could figure out what is going on!


Different color of blue. Do you use a copper based algaecide or have an ionizer system by any chance? Also how are you testing pH?

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  • 8 months later...

This is 100% the filter end caps with the soft grip “dissolving” from imbalance. Watch out because it doesn’t redesolve with filter cleaner and has to be manually sprayed or scraped off. Also, watch out for clogged lines after this and blocked sensors on pumps and thermometers. And honestly, it’s probably due to a change in material by a Chinese manufacturer. I’ve seen it many times before. 

Edited by EricHei
Wanted to add root problem.
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