White chalky substance on walls of fiberglass pool

al27

Well-known member
Sep 11, 2017
85
TN
When I rub the walls of our fiberglass pool, a white chalky substance comes off on my hands. When I brush the walls, it clouds up the water. I called the manufacturer and was told that it was caused by too low calcium, too high PH, and high chlorine levels. They recommend a calcium level of 350, PH of 7.4, and chlorine level of 1-3. This year, I've been keeping my chlorine at 5, calcium has been around 150-200 and PH tends to stay around 7.6-7.8. I was advised to increase my Calcium to 350, be more diligent about keeping PH lower and decrease my chlorine level to 3 or lower. They recommended that I use a calcium scaling product to remove the scale. I was getting ready to close the pool in a few weeks so I'm wondering if I should raise the calcium level now and use the descaler product before we close, just add calcium now and wait to use the descaling product in the spring, or just close with the calcium levels lower and postpone doing anything until spring. Will the calcium scaling get worse or damage the gelcoat if I close the pool with low calcium levels? If I don't remove the scale, would bumping up the calcium level to 350 preserve the gelcoat over the winter? I was told that the calcium scaling product might take several months to work and I don't have much time since we plan on closing in 2-3 weeks so I don't know if it is worth trying it.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
43,998
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Realize the levels they state for the water chemistry are standard pool industry levels. Nothing specific to fiberglass pools. It makes no sense to say you need to raise your calcium level but that you have scale.

My fiberglass pool does not have the white chalky substance. Now my CH is always way above 350 (near 1000 ppm right now), my pH ranges from 7.2 to 7.8 and my FC is always at 5 ppm or above.

I would suggest using the search box above for "fiberglass white chalk". Lots of hits on this forum. None are correlative to water chemistry.


What age is the pool shell?
 

al27

Well-known member
Sep 11, 2017
85
TN
The shell is approximately 13 years old. I searched the forums and saw several posts from people who had the same problem with their pool from the same manufacturer (Sun Fiberglass Pools). It sounds like I need to get calcium up to 300, keep PH lower and use the Scaletec product they recommended. it is supposed to take weeks or months for the Scaletec product to work so I'm wondering if I should bother trying it if I plan on closing in a few weeks. If I increase calcium to 300 and keep PH at 7.4 until I close in two weeks without using the Scaletec, will the scale increase since calcium levels will be higher over the winter and be more difficult to remove in the spring? I'd like to remove the scale before we close but I've already scheduled my closing so it might not be possible. It's also going to be extremely difficult to keep the PH below 7.6 to prevent scaling since I have a saltwater generator that keeps PH around 7.8-8.0 most of the time and creeps back up quickly after muriatic acid is added.
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Jun 22, 2014
33,424
Texas, San Antonio/Marion, South-Central Area
Pool Size
17888
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-45 Plus
I'm not so sure what you are wiping off with your hands is calcium. Because I had an exhausting chalky experience with my pool, I also saw some of those threads/posts where a few owners increased the CH level to 300-350 and the white stuff disappeared. But I think their situation was different than calcium scale which we see as hard to remove. The stuff they had was simply wiping off and may have been some stage of oxidation. While we typically look at FB (and vinyl) pools as not requiring much CH because they are not fabricated with plaster anymore, I believe there is a buffering content that helps protect the gelcoat a bit. I disagree with the high chlorine comment from the manufacture though as the stabilizer in your water will adequately protect everything from the chlorine when balanced as noted on the [FC/CYA][/FC/CYA]. The ScaleTec they are recommending is generally used to remove hardened scale which you do not appear to have, so I'm not so sure you'll reap the benefits of using it at ~ $35 per bottle. Some of those other owners seemed to correlate the use of ScaleTec and increased CH to the chalkiness going away, so it's certainly your call.

You mentioned the CH level increasing in the winter, but actually the CH doesn't go up. The pH rises slightly, but the water temp counters it, so really your CSI level (see PoolMath) remains about the same. I would agree with your concept of increasing the CH to 300 though only because others have had positive results with the same issue, while also making sure the pH is in the mid 7s with a reasonable TA as well - somewhere between 60-90-ish. If you had scale forming, it would be hard, crusty, and difficult to remove. If you lower the water level at closing and can expose some of the chalkiness, try spraying some muriatic acid on it. If it fizzes, it's scale. But if it doesn't, I suspect it's a type of oxidation. As long as your CSI is in the slightly negative range (-0.1 to -0.3) you should not experience any new scale issues.
 

al27

Well-known member
Sep 11, 2017
85
TN
I talked to a fiberglass pool pro about my problem and he said that some older fiberglsss pools like mine will experience extreme chalkiness if calcium levels are very low and PH stays too high. Every time I tested PH this summer, PH was between 7.6-8.0 and would creep right back up a day or two later so imagine that PH has been high or in the high end of normal all season. Calcium Hardness was also very low all season and is currently at 150. I'm getting ready to close in two weeks so I think I will bump up the calcium level to 300 and see if that helps any. I've been told that low calcium levels can cause staining so it would probably be a good idea to increase the level before closing anyway since algecides that cause staining will be added and the pool might turn into a swampy mess over the winter. It doesn't sound like I've got time to try Scaletec after I get the calcium levels up since I'm getting ready to close and it takes awhile to work. Do you think the problem will get worse if I increase the calcium to 300 without using the Scaletec before closing? I'm eager to close before leaves start dumping into the pool but could possibly delay the closing if I need to take care of this chalkiness first.
 

YippeeSkippy

Mod Squad
LifeTime Supporter
Jan 17, 2012
17,536
Evans, Georgia
How old is your pool, and are you the original owner?

I ask because I'm curious to follow this and see if there is a trend. My pool is 7 years old and I do not have any chalky stuff on my walls to wipe off. We initially had low CH but it has been around 200-250 since year 2.

Maddie :flower:
 

al27

Well-known member
Sep 11, 2017
85
TN
How old is your pool, and are you the original owner?

I ask because I'm curious to follow this and see if there is a trend. My pool is 7 years old and I do not have any chalky stuff on my walls to wipe off. We initially had low CH but it has been around 200-250 since year 2.

Maddie :flower:

My pool is approximately 13 years old and I'm not the original owner. I think the calcium level has been low a long time because the fill water here doesn't contain much calcium. A fiberglass pool pro told me that a lot of older fiberglass pools have calcium in the gelcoat and they will chalk like this if calcium is too low and PH is too high. He said that he sees it in pools with salt water generators more often because they tend to have higher PH. I've been advised by the manufacturer to get the level up to 300-350 to prevent this from getting worse which I'm going to try to do before we close it. I'm curious to know if anyone has experienced this problem and it went away after increasing calcium levels. I just don't have time to do the Scaletec treatments before we close so I'm hoping that increasing the calcium level and keeping PH lower will help some.
 

mkolb

Well-known member
Jun 1, 2018
68
White Lake, Michigan
I have the same issues; white chalky substance comes off when you rub or brush the pool. PH: 7.6, CH: 350, CYA: 70, FC: 9, TA: 100; so I personally don't think it has anything to do with the chemicals.. I really don't think its a huge issue, so I have just been dealing with it. Could this cause any harm to the pool?
 

YippeeSkippy

Mod Squad
LifeTime Supporter
Jan 17, 2012
17,536
Evans, Georgia
I have the same issues; white chalky substance comes off when you rub or brush the pool. PH: 7.6, CH: 350, CYA: 70, FC: 9, TA: 100; so I personally don't think it has anything to do with the chemicals.. I really don't think its a huge issue, so I have just been dealing with it. Could this cause any harm to the pool?

Just for curiosity sake- how old is your pool?
 

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bljamison

Silver Supporter
Bronze Supporter
Jul 17, 2019
19
SW Oklahoma
I have a two year old Trilogy Fiberglass pool and had this problem last summer (2020). At that time, I maintained FCH at about 5ppm, my PH was 7.5, TA was 120, CH 280, CYA 43. After some adjusting and with time (a month later), my numbers were about Fch 5.0, PH 7.7, TA 105, CH 370, CYA 45. I had no more chalky stuff that wiped away into small little flakes. In this time, we also cleaned the cartridge filters. It appears decreasing TA and increasing CH helped, along with cartridge cleaning.
 
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