fiberglass pool walls are chalking


Active member
Oct 21, 2018
Northern Tennessee
When I rub my hands along the walls of my fiberglass pool, I get a chalky white substance on my hands. This has been happening all season but it seems to be worse lately. I called a fiberglass pool pro about it and he said it is a common problem with older fiberglass pools like mine, and it is usually caused by low calcium, high PH, and high chlorine levels. He recommended that I increase calcium to 300, decrease ph to 7.4, and keep chlorine no higher than 3 ppm. Does this sound like good advice? Right now, calcium is 220, PH is 7.6-7.8, and I keep chlorine at target level (4-5). Has anyone else experienced this problem and did the problem go away once you increased the calcium and lowered PH and chlorine levels? Since the water is too cold to swim in right now and we plan on closing in 2 weeks, do we need to increase calcium levels before we close or can this wait until next Spring?

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Jun 22, 2014
Texas, San Antonio/Marion, South-Central Area
Pool Size
Salt Water Generator
SWG Type
CircuPool RJ-45 Plus
He recommended that I increase calcium to 300, decrease ph to 7.4, and keep chlorine no higher than 3 ppm. Does this sound like good advice?
Not really. In general, we want water that is not too "aggressive" which may harm the gelcoat, but also don't want it too "hard" which can result in scale. Best thing is to use our PoolMath tool. Once you enter all your test results (and water temp) it will give you a CSI number.. While CSI is thought primarily to maintain healthy plaster in pools, it also tells us FG and vinyl owners what the overall chemistry looks like. Try to adjust CH, TA, and pH so that those, along with water temp, keep the CSI about neutral.

If you search our forum, you'll see there are varying reasons and degrees of FG chalkiness. Some (like you) say they can rub their hand along the shell and the stuff literally wipes-off. Others (like me) find it does not wipe off, so some scenarios are different. For those who say their chalkiness wipes-off, I recall some saying that when they increased their TA it helped. But I say that cautiously because if their CH and pH are already in a good place, a low TA shouldn't really matter if the overall "CSI" was good.

The FC should not be an issue if it is balanced to your current CYA as noted on the FC/CYA Chart. The "no higher than 3 ppm" comment is an old industry standard without taking into consieration the stabilizer (CYA) level to prevent algae.

If you decide to increase the CH level in an effort to see if it helps, I would still watch the pH and TA. A higher CH means the TA and pH cannot be allowed to go too high (scale). Let us know what you do and how things work out. Good luck on your closing.
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