Help - Dull ring around fiberglass pool water line

dmcconnell68

Well-known member
Jul 15, 2017
68
Fort Worth, Texas
Hi,

Can anyone tell my what causes this dull ring around the water line of my fiberglass pool and how to get rid of it? The pool is just under 2 years old and I have this unsightly ring that I cannot get rid of. I can wipe the scum/oil off with a rag and it comes right off, I can see it on the rag. This is something different. I have tried magic eraser, wipe out, etc but nothing seems to touch it.

FC: 3
TC: 3
CC: 0
PH: 7.6
TA: 90
CH: 200
CYA: 50
Salt: 3800 per Taylor test kit. I know it should be around 3200, but at that level, the salt cell complains of low salt.

Thanks,
David


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Last edited:

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
I have the same thing. I believe this to be the natural oxidation process that takes place from seasons of blistering hot TX sunshine reflecting off the water and ultimately dulling the original gelcoating. Looks fine once you wet it, but once it dries it has that faded appearance - much like an old car hood. If it really bothers you, there are some FG polishing products out there (marine-grade) that help to restore glecoats. Some people might try a very fine wet sandpaper (1000 grit or more) which may help to remove a very thin layer of oxidized gelcoat to expose the original. Our shells are quite durable. But if you try that method, always try a very small test area first, let it dry, and inspect closely to make sure it didn't have any ill effects and that you are pleased. Last but not least, some FG pool owners will have a waterline tile installed with something that will tolerate the heat better and to spruce-up that waterline.
 

sktn77a

Gold Supporter
May 16, 2010
1,292
Chapel Hill, NC
Have you tried CLR on a small area? It could be either scale/dissolved solid residue, or oxidized gelcoat. CLR will get rid of the former. Not sure about the latter.
 

dmcconnell68

Well-known member
Jul 15, 2017
68
Fort Worth, Texas
I have the same thing. I believe this to be the natural oxidation process that takes place from seasons of blistering hot TX sunshine reflecting off the water and ultimately dulling the original gelcoating. Looks fine once you wet it, but once it dries it has that faded appearance - much like an old car hood. If it really bothers you, there are some FG polishing products out there (marine-grade) that help to restore glecoats. Some people might try a very fine wet sandpaper (1000 grit or more) which may help to remove a very thin layer of oxidized gelcoat to expose the original. Our shells are quite durable. But if you try that method, always try a very small test area first, let it dry, and inspect closely to make sure it didn't have any ill effects and that you are pleased. Last but not least, some FG pool owners will have a waterline tile installed with something that will tolerate the heat better and to spruce-up that waterline.
Thanks for the info. I am planning to get someone out here to put on waterline tile. I guess I just need to quit procrastinating and make the call.
 

dmcconnell68

Well-known member
Jul 15, 2017
68
Fort Worth, Texas
Have you tried CLR on a small area? It could be either scale/dissolved solid residue, or oxidized gelcoat. CLR will get rid of the former. Not sure about the latter.
Hmm.. I hadn't thought of CLR. I may give that a try this afternoon. Would be nice for it to look better until I get waterline tile installed.
 

CPS Reno

In The Industry
Feb 6, 2019
28
Reno, NV
This "dulling" of the pool surface is something that I talk to with every one of our new pool customers. Most of our pools are sold with tile, but about 25% are not. My only warning for fiberglass pools without tile are that the sun can change the color of dull the finish above the waterline. Our pools have a great finish, but the Sun can do things that humans just haven't figure out how to stop yet. I'd be interested in your solutions, though.
 

dmcconnell68

Well-known member
Jul 15, 2017
68
Fort Worth, Texas
I wish my builder had shared that information. My back yard has full Texas sun from about 10am until 8pm. Since I haven't really found a chemical solution, I'm going to have to get someone to install water line tile. Can I ask a question you may know the answer to? My pool has cantilever concrete coping. How hard is it to cut enough of the concrete out to maybe do a real stone border and extend just a bit more into the pool to cover the top of the tile?

Thanks,
David
 

Winger 03

Well-known member
Sep 7, 2009
223
Frederick County, MD
It is a little hard to see but my bet is that in order to to get it to look right with tile you will have to do a full coping replacement. There does not seem to be enough cantilever with the current coping to be able to install tile. We went through this process this Spring due to our coping having never been right and took that opportunity to install tile during the "remodel". Our fiberglass pool had the same "dulling" above the water line as well (we are at 10 years old) - looked fine when wet, awful when dry. Tile has solved that problem for us.
 

dmcconnell68

Well-known member
Jul 15, 2017
68
Fort Worth, Texas
Thanks Jim for the info. Can you tell me what the process is to do a full coping replacement? I assume they cut the existing concrete out? Is there any risk of pool shell damage during this process?
 

duraleigh

Admin
Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
In The Industry
Apr 1, 2007
32,584
Sebring, Florida
In a small area, I would try a mixture of 2:1 water and muriatic acid. It looks like calcium deposits to me and the acid/water mixture will remove it. Whether or not the surface is already damaged is hard to tell. If it is, the muriatic I guess could make it a bit worse.

Again, try it in a small, out of the way area.
 

Winger 03

Well-known member
Sep 7, 2009
223
Frederick County, MD
It was a mess! There was a joint where the coping met the deck. To be honest I cannot recall if they used a grinder to make that joint deeper and more pronounced. But they did use a jackhammer to break up the coping. To me they could have been a lot more careful in not letting big chunks fall in. When they saw what was happening, they took my looploc safety cover and did their best to line the bottom of the pool with it to catch debris. It worked, but not very well. There were pretty large sized pieces in the water, remarkable, no scratches after all was said and done.

So during cleanup, I see the guy using a normal vacuum on a pole and the hose into the port under the skimmer basket. That bothered me because there were pieces smaller than a golf ball with jagged edges that I KNEW would get caught in the pipes. I asked him "dont you think a skimmer plate might be a little better" He said, "this is going well but every now and then the hose gets clogged with rocks". Well, darn, no kidding, imagine what is in my pipes.

They came pout a couple of times to clean, never got it to my satisfaction and I was more than happy to go at it on my own with a skimmer plate and the vac hole taped to the pole since I did now want to drag pieces of rocks under the vac head.

All in all, it got done, looks better and we are none the worse for wear. I would have appreciated a little more thought on the project beforehand and a little more detain on applying the tile. There is a part that is not quite symmetrical that only I see but the fix was so simple if they would have given it some thought ahead of time.


Thanks Jim for the info. Can you tell me what the process is to do a full coping replacement? I assume they cut the existing concrete out? Is there any risk of pool shell damage during this process?