Fiberglass pool walls no longer smooth under waterline

Graul95

Member
Jun 17, 2020
13
Ohio
Hi all,
The walls of my 3-year-old fiberglass pool have a texture under the waterline compared to the smooth texture above the waterline. It's not like sandpaper grit or chalkiness but there's a definite texture that doesn't belong there and wasn't there for the first couple years. There is no change after vigorous brushing and scrubbing so not sure if it's a residue/scale that has built up or if it's some kind of erosion or pitting of the gel coat. I have been brushing ~weekly.

Here is my chemistry:
visual: clear water
FC: 7.5 (currently a little high as I've recently been battling some persistent haziness; on the way down to my target of 5)
CC: 0.5
pH: 7.6
Alk: 100
CYA: 70
CH: 250
Temp: 82F
Sat index: +0.1

I needed to SLAM twice this year to control cloudy water. For that I used cal-hypo but otherwise I use my SWG as my chlorine source. It's not clear to me whether the cloudy water issue is somehow connected to the wall texture issue, as I'm currently thinking the cloudy water was due at least in part to an aging and dirty filter since the cloudiness went away without SLAMing once I replaced the CC200 filter.

I've read though some of the other threads here relating to fiberglass pool shell problems but haven't found anything that sounds specifically like my problem. I don't see any visible sign of what I feel and I can't scrape off any residue. That said, I gather the most likely explanation is some kind of scale, but how do I test for scale below the water line? Are there any other tests I can do to investigate the cause?

Thanks
 

Graul95

Member
Jun 17, 2020
13
Ohio
Thanks Texas, I will try that. I can't feel the abnormal texture on the horizontal surfaces of the steps or floor because they are textured themselves, but I will try adding acid to the wall above the first step. With the heat this week it shouldn't take long to drop the level!
I do not notice any change in color.
 

Yev

Well-known member
Jul 29, 2014
558
Independence, KY
To test for scale, Viking had me lower the water level to expose the first step and pour muriatic acid on it to see if it reacted (fizzle). Besides the change in feel, has the color changed at all?

Lets say that OP lowers level and it does NOT fizzle. This would rule out calcium scale I would assume. Are there any other likely causes for roughness on the walls?
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Jun 22, 2014
40,592
Texas, San Antonio/Marion, South-Central Area
Pool Size
17888
Surface
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Chlorine
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SWG Type
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Are there any other likely causes for roughness on the walls?
With no color change, I can only assume the gelcoat itself has changed/adapted for some reason due to effects of being underwater. Might be something the OP discusses with the manufacture.
 

Graul95

Member
Jun 17, 2020
13
Ohio
Update... I dropped my water a few inches and added muriatic acid down the side of the wall and didn't see any bubbling reaction or any difference in the texture afterwards. I also took my water to a pool store for testing on the off chance that what I'm feeling is metal staining but iron and copper were both zero. Other results were close to my own. The only surprise was my salt level is slightly high at 3602 ppm. I don't routinely test for salt and have just used the indicator on my SWG to let me know when it's in the appropriate range. I told the pool store manager my issue with the texture change and she took one look at my results and told me confidently that the issue is salt scale on the walls and to use stain and scale remover. I know calcium scale is common with SWG and FB pools but is there such a thing as salt (sodium chloride) scale? If so, wouldn't that be able to be scrubbed off with a brush? I suppose I'll try the stain and scale remover but I'm not super hopeful.

My current theory, in line with Texas Splash's comment above, is that something happened to the surface of the gelcoat during the winter. With all the cautioning from manufacturers to keep your water constantly balanced for the health of the pool surface, it doesn't make a lot of sense to me that the water can just sit there stagnant for 6 months over the winter with no testing or balancing, especially for alkalinity and ph. I certainly did not receive any guidance from my builder or even the manufacturer via the manual to do much of anything between closing and opening. My water at opening this year was very low in both alkalinity and ph and I'm concerned that has caused corrosion of the gelcoat. One of the main reasons I went with fiberglass over gunnite was the supposed durability and low maintenance aspect of FB, and if that is what ends up being a serious problem I'm going to be one unhappy customer to say the least.

Will update again after addition of the stain and scale remover.
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Jun 22, 2014
40,592
Texas, San Antonio/Marion, South-Central Area
Pool Size
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Chlorine
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I totally understand your feelings. :brickwall: While gelcoats are understood to be somewhat porous and accessible to chemicals over time, it seems as though some pools simply undergo changes we can't quite explain. Aside from some owners who really let their chemical levels get out of whack, perhaps some changes are due to the gelcoat manufacturing and/or application process. Not really sure. Your texture issue seems to be different than what I went through.

 

Graul95

Member
Jun 17, 2020
13
Ohio
Thanks TS, that's a great write-up and a super helpful resource for owners going through this so thanks for documenting your experience so thoroughly. Time will (hopefully) tell if my issue is scaling or corrosion or something else but either way it's a problem with the FB gelcoat on a 3 year old pool that has been maintained pretty well. I totally understand that that there are some things about gelcoat chemistry that might not be 100% understood even by the manufacturers but I'm starting to feel like some of the potential problems and risks were not disclosed up front by the builder and manufacturer and that is unacceptable. I heard a thousand warnings from the builder about not draining the water below the skimmer but never heard one thing about the risk of irreversible corrosion of the gelcoat. That is definitely something I would have wanted to know about and guard against at all cost.
 

Bperry

Gold Supporter
Aug 20, 2020
2,225
Knoxville, TN
Pool Size
27000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-60
Thanks TS, that's a great write-up and a super helpful resource for owners going through this so thanks for documenting your experience so thoroughly. Time will (hopefully) tell if my issue is scaling or corrosion or something else but either way it's a problem with the FB gelcoat on a 3 year old pool that has been maintained pretty well. I totally understand that that there are some things about gelcoat chemistry that might not be 100% understood even by the manufacturers but I'm starting to feel like some of the potential problems and risks were not disclosed up front by the builder and manufacturer and that is unacceptable. I heard a thousand warnings from the builder about not draining the water below the skimmer but never heard one thing about the risk of irreversible corrosion of the gelcoat. That is definitely something I would have wanted to know about and guard against at all cost.
If your CSI is over 0 consistently, then scaling is possible. Have you tried adjusting it to be slightly below 0? Your salt level isn’t very high. Have you tested it with a drop based kit? The reading on the SWG isn’t typically very accurate.
 

Graul95

Member
Jun 17, 2020
13
Ohio
If your CSI is over 0 consistently, then scaling is possible. Have you tried adjusting it to be slightly below 0? Your salt level isn’t very high. Have you tested it with a drop based kit? The reading on the SWG isn’t typically very accurate.

I don't have the salt test as part of my kit but I did test at opening using a friend's kit. After adding a few bags to adjust to the target I haven't adjusted since the light on my SWG says that it's fine. Even if salt is high, is salt scale on pool walls a thing?

As far as CSI, my overall readings never got out of control to the point that I was worried either positive or negative, at least not for an extended period. Other than, of course, the 6 MONTHS the pool sits without any balancing or testing. During that time, I'd expect the CSI to drift lower, as evidenced by the fact that my ph and alkalinity were very low at opening. I'm hesitant at this point to make any adjustments to the CSI without knowing whether I have scale or erosion/pitting since if I guess wrong I could make it worse.
 

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Bperry

Gold Supporter
Aug 20, 2020
2,225
Knoxville, TN
Pool Size
27000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-60
I don't have the salt test as part of my kit but I did test at opening using a friend's kit. After adding a few bags to adjust to the target I haven't adjusted since the light on my SWG says that it's fine. Even if salt is high, is salt scale on pool walls a thing?

As far as CSI, my overall readings never got out of control to the point that I was worried either positive or negative, at least not for an extended period. Other than, of course, the 6 MONTHS the pool sits without any balancing or testing. During that time, I'd expect the CSI to drift lower, as evidenced by the fact that my ph and alkalinity were very low at opening. I'm hesitant at this point to make any adjustments to the CSI without knowing whether I have scale or erosion/pitting since if I guess wrong I could make it worse.
Not likely to have salt scaling under water. On the deck is theoretically possible after evaporation but I’d imagine the salt content would have to be be super high for it to come out of solution while under water. You don’t see salt scaling in anything at the beach. (Unless it’s the salt ponds where they are trying to get salt)
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
51,244
Laughlin, NV
Pool Size
6000
Surface
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Chlorine
Salt Water Generator
SWG Type
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There is no such thing as 'salt' scale.
It can be scale that is not as susceptible to acid, but those are rare in a pool water environment.
 
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csconner

Bronze Supporter
May 8, 2020
121
Nashville, Tn
Pool Size
8000
Surface
Fiberglass
Chlorine
Salt Water Generator
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Graul95,

I have a similar experience With my FG pool. I’ve discussed here several times.

my belief is I did not use TFP first 1.5 years

i have the white spots/scale/surface degradation on pool walls and floor but it’s not consistent across the pool, does not correlate to sun/less sun, deep, shallow, near, far from returns, etc.

since adopting and applying TFP “white scale” has not changed.

my speculation is since I did not use TFP in the early days and ran the SWG at 50-60% and added no CYA and no calcium, this “damaged” the pool surface.

similar to TexasSplash’s efforts I can positively impact the scale on a small scale using magic eraser (have not tried sand paper). But the result vs level of effort is insignificant.


as I stated, once I adopted TFP there’s been no further degradation of the pool surfaces.

my $.02

craig
 

Nannyspool

New member
Sep 22, 2022
2
Australia
With no color change, I can only assume the gelcoat itself has changed/adapted for some reason due to effects of being underwater. Might be something the OP discusses with the manufacture.
I have exact white oxidising as you explained in earlier post. I am about to start sanding with 120 wet and dry as you noted. Wish me luck. I've done a small patch and it has bought color back to dark blue so I think you have provided me the answer when the experts plus $1000 later have not been able to. I thank you 😁🤙
 

Bperry

Gold Supporter
Aug 20, 2020
2,225
Knoxville, TN
Pool Size
27000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-60
I’m curious if anybody has tried this product/service?

I have not. But your pool math logs show your water spent some decent amount of time with high CSI 3-6 months ago. You might try holding it at CSI less than zero like has been recently and see if the scaling clears up. I suppose scaling above the waterline may not be affected by that though.
 
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