Lowering PH cleared cloudy water - Does this indicate some other problem?

[heugeneo]

I'll post the initial numbers before I go into the question:

FC 8
CC 0
PH 7.4
CH 425
TA 175
CYA 90

Since I got the CYA down from 500 everything had been good with the water. I have kept FC between 6-8 (I know, maybe a little low but wanted to be able to test PH). I normally keep the PH between 7-7.2 due to metals in the water.

Last Sunday we had a lot of people in the pool, a large rainfall of 2" (don't roll your eyes Texas people), and I added some Metal Magic. Every day after that the water got slightly cloudier. I slowly raised the FC level until a high of 12. I performed an OCLT every night which passed each time and never had a CC of more that .5 over the time period. I read one thread in which Jason had commented that high PH+TA+CH can cause cloudy water. As you can see the PH wasn't really high, just higher than I normally have it. So I put the recommended amount of muriatic acid in to get down to 7.0 last night. I got up this morning and viola, water is clear again.

So what gives? Does lowering PH normally clear the water in and of itself? Could I have had an algae bloom trying to start even though there was no overnight chlorine usage? Does metal magic or other sequestrants cause cloudy water?

Thanks for any insight.

 

[heugeneo]

 

[pooldv]

Sorry we missed this.

My hypothesis is that chlorine is more efficient at lower PH. Had you raised the chlorine level you would have achieved the same results. I don't know anything about whether sequestrants can cause cloudiness.

 

[jblizzle]

With CYA in the water, the chlorine effectiveness is not changed much by the pH in the normal ranges, so that does not seem like the issue.

Calcium clouding can happen at higher pH, although you pH did not really seem high enough for that.

 

[TreeFiter]

I had an experience with a pool once, where a sequestrant was causing the calcium in the water to precipitate. I don't know exactly why it does this in some pools, but not others, but with CH at 425, there would be plenty of Calcium for the sequestrant to grab onto and precipitate.

I don't think this odd situation had anything to do with pH affecting the potency of the FC. When there is cyanuric acid present, the influence of pH is diminished significantly. If I remember correctly, the difference it makes at 30ppm CYA is something like the equivalent of 0.1ppm FC. At 90ppm CYA the difference would be far less.

You could retest the Calcium Hardness now that it has cleared up to see if it has decreased any. If the CH has decreased, the sequestrant likely caused some of the calcium to precipitate and filter out.

 

[chem geek]

The Calcite Saturation Index, which you can calculate using PoolMath was +0.32 assuming the water temp was 85ºF. I suspect that your pH is in fact higher than you reported given your high 175 ppm TA, unless you recently added acid or have been using Trichlor pucks. With people and rainfall I'd expect the aeration to have the pH go higher. Normally we don't see scaling until around +0.7, but it's possible that if the pH was actually higher that it could get cloudy or at least dull-looking.

Another possibility is that the Metal Magic bound to metals and clouded the water since it is designed to try and coagulate and filter out metals from the water. It's possible that lowering the pH reduced that effect or that coincidentally got filtered out around the same time you lowered the pH.