Can Pool Chemistry Cause Extreme Chalking of Fiberglass Pol's Gel Coat? Milky water

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etbrown4

Well-known member
Feb 24, 2012
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I'm working on 2, that right 2 identical fiberglass 15,000 gal inground pools, with extreme chalking problems so bad that they both plug their respective sand filters within 4-6 hours.

Both were clear upon opening last week, but have begun encountering extreme chalking of the gel coats in both.

The pools were fine last season. they are 10 yrs old.

Has anyone experienced this, and if so did you find something in the chemistry that caused it?

Tips appreciated!
 
Can Pool Chemistry Cause Extreme Chalking of Fiberglass Pool Gel Coat? Milky water

JamesW said:
Can you post a full set of test results?

Has either pool been painted or regellcoated?
Click to expand...

These are 2) 10 year old pools with all original finishes. They were fine last year and stayed clear all winter.

They were clear until last week.

The very experienced pool man helping me, informs me the PH is normal, Chlorine is about 5ppm, and the CYA is about 50, beyond that, I'll have to get more results.

Pool man has 25 years experience and is confident the fault is with my pools and their gel coat.....but they were fine last year, and fine until a few days ago, now milky and backwashing required every 4-6 hours, or a plugged filter..

So the burning question is can any bad chemistry number attack the gel coat? Have you seen it? What chemical should we especially look out for as a possible culprit, as I'm in bad shape now and getting worse?

Help is much appreciated.
 
I think I have seen mention in the forum that in low quality gel coats, if the CSI is too low (low CH, TA, pH, etc) calcium can be pulled out of the surface. But I don't think that would clog the filter.

More likely that you FC got too low relative the CYA and algae started and is being killed off clogging the filter.

Do the OCLT to prove or disprove it if you have one of the recommended test kits.
 
Re: Can Pool Chemistry Cause Extreme Chalking of Fiberglass Pool Gel Coat? Milky wat

etbrown4 said:
they were fine last year, and fine until a few days ago, now milky and backwashing required every 4-6 hours, or a plugged filter..
Click to expand...
If they have been fine for so long and suddenly, there's a problem, then I don't see how the quality of the fiberglass is the issue.

If the quality were poor, then the finish would begin breaking down fairly soon and progressively. I don't think that it could happen suddenly.

I would first suspect algae or scale, but there is not enough information to tell, yet.
 
Can Pool Chemistry Cause Extreme Chalking of Fiberglass Pool Gel Coat? Milky water

Ok so the plot thickens!

We had a clear pool last week, and my pool man has determined that swimmers in the pool have rubbed the walls and caused the chalking fiberglass to cloud the water.

Sure enough, if you wipe the side with your hand, there is a definite white residue. It puzzles as this pool has performed just fine for the last 10 years, until now.

I've run into 2 independent pool techs who suspect low calcium as the cause. Both say they have definite experience with this problem, and both say that when they got the calcium right, the chalking stopped on white fiberglass pools!

So here is the chemistry...
Ch 5
ph 7.6
Cal 100
Hardness 100
Alk 130

Has anyone on this forum experienced this?

Will keep you posted on progress

These figures are on the one pool which is chalking the most, as we have 2 identical side-by-side pools. The other pool has milder chalking and coincidentally the Cal level there is 150 !

We shall see.
 
The cya is high at 120 and either the free or total chlorine was between 3 and 5. I know the cya has to be lowered.

I've chatted with Dave the forum owner on this, and though we're all making educated guesses at this point, he feels that it's not organic. Still It's possible.

The two independent pool techs who do this full time in the area, and have 35 yrs experience between them both have experienced high chalking on fiberglass pools. And they both solved the problem by raising the calcium! I had thought that calcium was most important in concrete pools, but if this proves out, it could be structurally or economically important for fiberglass as well.

I'm hoping some guys on this forum have experienced the same kind of chalking, and am looking forward to how they cured it!

Just not ready to spend the $25k for another inground fiberglass pool or to gel coat this one, just yet. Though I get the feeling that if this condition is allowed to persist, it seemingly could cause long term damage, as that white stuff is almost definitely dissolved gel coat!.......though until it's for sure, I'll keep an open mind.
 
With high CYA levels I'd still lean towards organic being the cause personally. The majority of the time, cloudy water means algae is slowly starting to form. An OCLT will eliminate this as being an issue from the list.
 
I know that anything is possible. When I can get a test kit, I'll try it the test.

As for the chalking, it's white, the same color as the fiberglass. When there is no swimmer load the water is clear.

My pool guy is convinced that with this pool and others he has seen it's swimmer contact with the walls or wave action in the pool that clouds the water. He could be mistaken, though I think he is right.

Has anyone seen this type of chalking that will put a white film on your hand if you rub the wall - even in a completely clear pool?

I posted this over on gardenweb's pool forum too, and one pool guy there...making it now 3, says that calcium is the likely culprit based on his experience.

It's not the final word, but it's becoming convincing.

We shall see.
 

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I'd like to start off by saying I have little experience with fiberglass, so my statements maybe slightly off.

There is a filler used in the manufacturing of some fiberglass pools that low calcium levels can cause a harm. If your pool has this filler, there is danger having low CH levels. Without this filler low levels are fine. This is why we say however to treat fiberglass pools like a plaster pool, as there's simply no way to know for sure what was used during production.

While this is something that CAN happen, and something we've seen before.....I'd still push checking organics before doing anything drastic (expensive).
 
I have a concrete pool that has the same reaction to the breakdown of paint. My pool will be crystal clear, even diamond flickering, then when a few swimmers get the water moving, the chalking starts and creates milky pool water within an hour. This has been going on ever since I used Poly One Coat ten years ago. The manufacturer has given me paint four times.... Since I live in the town where it's manufactured, they had chemists out to check my chemistry. They Even paid to have their painters paint it. It stilled chalked within months! They are willing to give me more paint, but I give up.

Since doing my own testing last year, and reading on TFP, I raised my CH up to 120. It did lessen the chalking considerably. My Pentaire DE filter works great at clearing the chalk out of the water. (I had a new cartridge filter installed last year. I returned it because it just couldn't get the chalking residue out of the water.) I have read on this site that you can add some DE to a sand filter.

Even though mines concrete, the symptoms seem to be the same.


Sent from my iPad using Tapatalk HD
 
With fiberglass, it really depends on what is used in the gel coat. If it doesn't contain significant amounts of calcium carbonate, then saturating the water with calcium carbonate isn't going to help, but if the gel coat does contain calcium carbonate, then saturating the water could help. It basically comes down to whether the surface of the pool has calcium carbonate at its surface.
 
If rubbing the wall leaves a white residue on your hand, it's probably the finish breaking down. Paint and fiberglass can both do this. Once it happens, you're probably going to have to refinish the surface to resolve the chalking problem. Maintaining a neutral to positive CSI might help some. However, it probably won't make a big difference.
 
OP here - Thanks to all posters for the helpful info.

I found the following information on another site, which may prove helpful....especially if the low calcium theory proves out.

"Any high levels of chalking on a fiberglass pool is likely indicative of very low calcium. Don't be surprised if the ladder treads break (if you have one). Bring the calcium level to 200 ppm. Unfortunately, once it comes off, it can't go back on, but maintaining proper calcium levels and keeping the pH in check (consistent high pH will result in calcium "drop out") can prevent further damage. Keep brushing with a nylon brush and if you've balanced the water, it should be filtered out in a week or so."

With these problem fiberglass pools, we're starting to add calcium today! will post the results.
 
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