Fiberglass pool; possible oxidation; calcium - questions!

SarahMili

Active member
Dec 30, 2018
35
Glen Rock, PA
We’re in our 3rd season with our fiberglass pool. Started following TFP method religiously mid-season last year.

Recently our water level dropped a few inches due to evaporation, and I realized there was now a white coating on the exposed fiberglass surface when it’s dry. It’s not above the normal water line, and it disappears when wet. It doesn’t feel rough. I started to panic and have now read though many past threads on here about similar issues. After reading others’ experiences, I’m unfortunately leaning towards oxidation. Nothing chalky rubs off or clouds the water. Can’t imagine it’s calcium.

Based on the experiences I’ve read in others’ similar posts, I’m thinking I need to raise my calcium hardness to around 300 (currently is only 150). I’ve never worried about testing CH or adding calcium to the pool before. I had double-checked with the manufacturer to ensure that my fiberglass did not contain calcium filler or whatever (I knew the right term at the time), and I felt confident I could disregard calcium hardness. That said, we have hard water and turn off our softener whenever we add water to the pool, so I was a little surprised to see that my CH is only 150.

This brings me to my first question: what would be the best way to add calcium carbonate? Would you dissolve it one measly pound at a time (I need to add upwards of 40 pounds), or should I just dump it in a bit at a time and brush it around to try to dissolve it? Could this damage my fiberglass? I bought rock-salt, so it isn’t flakes. I read about the heating issue and understand I can’t dissolve more than 1 pound at a time.

Next question: It also seems like I need to start keeping my alkalinity higher, like in the 80-90 range. I’m curious why pool math lists my recommended TA range as low as 50 for a fiberglass pool. I’d been typically keeping it around 60-70.

Last question: if I do have oxidation already happening, is the only way to reverse it by sanding? I think I know the answer to this. :(

Any input about any of the above information is greatly appreciated. I’m so grateful for everything I’ve learned here, but clearly my learning process is still far from complete.

Just for the sake of being thorough, my current levels are:

FC: 7
pH: 7.9 (the struggle is real folks. I add muriatic acid practically every other day)
TA: 90
CYA: 40
CH: 150
 

Newdude

Gold Supporter
TFP Guide
Jun 16, 2019
10,346
NY
Any input about any of the above information is greatly appreciated
Your numbers are perfect.

You do not need calcium. 150 is perfect for fiberglass. Raising the calcium *causes* scaling if it’s too high, not too low.

Leave the TA alone if it’s between 60 and 110. It will find its own happy place.
pH: 7.9 (the struggle is real folks. I add muriatic acid practically every other day)
How much do you lower it ? Think of it as a swing. If you push the swing far, it comes back with a vengeance. Only lower to 7.6 when you do and it usually will take longer to climb again.

Also, and 7.X is fine. There is no good/better/best. Only adjust it when it hits 8. And only a little when it does.

People go nuts chasing their tails with TA and PH and it’s one of the pool stores biggest ruses. Sell you a bunch of stuff to put you on a wild roller coaster and keep bringing you back to buy more.
After reading others’ experiences, I’m unfortunately leaning towards oxidation
Very likely. The sun can really pick on certain peoples pools. Sometimes it’s nice to one neighbor and causes premature wear to the other one.
Last question: if I do have oxidation already happening, is the only way to reverse it by sanding? I think I know the answer to this. :(
Sorry to confirm. Besides sanding and new gel-coat there isn’t much you can do. @Texas Splash can explain further. :)
 

SarahMili

Active member
Dec 30, 2018
35
Glen Rock, PA
Your numbers are perfect.

You do not need calcium. 150 is perfect for fiberglass. Raising the calcium *causes* scaling if it’s too high, not too low.

Leave the TA alone if it’s between 60 and 110. It will find its own happy place.

How much do you lower it ? Think of it as a swing. If you push the swing far, it comes back with a vengeance. Only lower to 7.6 when you do and it usually will take longer to climb again.

Also, and 7.X is fine. There is no good/better/best. Only adjust it when it hits 8. And only a little when it does.

People go nuts chasing their tails with TA and PH and it’s one of the pool stores biggest ruses. Sell you a bunch of stuff to put you on a wild roller coaster and keep bringing you back to buy more.

Very likely. The sun can really pick on certain peoples pools. Sometimes it’s nice to one neighbor and causes premature wear to the other one.

Sorry to confirm. Besides sanding and new gel-coat there isn’t much you can do. @Texas Splash can explain further. :)
Hi! Thanks so much for the reply & all your insight! I had carefully read through Texas Splash’s experience and that was where I got some of my ideas including raising the calcium level. He said, “we can assume FB pools need no calcium because they were not made with plaster products, the CH and TA do play a vital role in keeping the pH and overall corrosive nature of water at-bay and from becoming too strong for the gelcoat” and mentioned that he was going to raise his CH to around 300 while also raising his TA to 80-90. But, ugh, I also don’t want to risk scaling!

As for the pH, I typically add 12-15 oz when it is 7.9-8.0 in order to target 7.6-7.7. For the future, I will back off unless it’s 8.0+ . The weird thing is that I just added 15 oz yesterday when it was 7.9, and then I checked it again this evening and it was already back at 7.9. 🤯 Unfortunately I had not had a chance to check it in between. I don’t think my acid is bad. 🤷🏻‍♀️

Thanks again; really value the input!
 
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Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Jun 22, 2014
32,954
Texas, San Antonio/Marion, South-Central Area
Pool Size
17888
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-45 Plus
Sarah, I can sympathize with what you're going through. I wish I had the perfect answer, but I don't. Unlike those other chalky posts who find the white film rubbing off with their hands, ours appears to be an embedded white, chalky discoloration that won't change unless physically sanded/buffed. It's odd because not all FG pools experience it. We do know gelcoats are permeable, so over time some changes can be anticipated. But for young FG pools like ours it's disappointing. What I would say is that if you do elect try try various chemical changes, just don't go too extreme. The TFP recommended levels are safe and gentle for surfaces as designed. For example, if it makes you feel better to increase the CH a bit, then just add a moderate amount (50-100). Don't add so much you set yourself up for scale later. Don't bother with fancy, miracle products because they won't work. Even though CSI should not apply to our FG (non-plaster) pools, I have been experimenting with mine to not let it get as low as I did a few years back when I thought I was seeing scale. I sand-tested an area about a year ago to bring out the original blue and seems to be holding relatively well so far. I've invested several years on this issue in our pool, and one thing I can emphasize is try not to let it get to you too badly. While the discoloration appears different based on location, time of day, and angle of the sun, no one knows or cares about it but you the owner. So if it's any consolation, try to enjoy your investment and don't driver yourself nuts. :crazy: I almost did. :) If we ever find a common denominator on this issue, we'll blast it out on the forum for sure.
 

Winger 03

Well-known member
Sep 7, 2009
343
Frederick County, MD
Sarah, I can sympathize with what you're going through. I wish I had the perfect answer, but I don't. Unlike those other chalky posts who find the white film rubbing off with their hands, ours appears to be an embedded white, chalky discoloration that won't change unless physically sanded/buffed. It's odd because not all FG pools experience it. We do know gelcoats are permeable, so over time some changes can be anticipated. But for young FG pools like ours it's disappointing. What I would say is that if you do elect try try various chemical changes, just don't go too extreme. The TFP recommended levels are safe and gentle for surfaces as designed. For example, if it makes you feel better to increase the CH a bit, then just add a moderate amount (50-100). Don't add so much you set yourself up for scale later. Don't bother with fancy, miracle products because they won't work. Even though CSI should not apply to our FG (non-plaster) pools, I have been experimenting with mine to not let it get as low as I did a few years back when I thought I was seeing scale. I sand-tested an area about a year ago to bring out the original blue and seems to be holding relatively well so far. I've invested several years on this issue in our pool, and one thing I can emphasize is try not to let it get to you too badly. While the discoloration appears different based on location, time of day, and angle of the sun, no one knows or cares about it but you the owner. So if it's any consolation, try to enjoy your investment and don't driver yourself nuts. :crazy: I almost did. :) If we ever find a common denominator on this issue, we'll blast it out on the forum for sure.
Us fiberglass owners who have this issue need an "Operation Warp Speed" type of research. I have a similar issue - the waterline time covers the visible problem, but I know it is there - lurking below the water.....
 

otter86753

LifeTime Supporter
Sep 26, 2013
618
Charleston, SC
Pool Size
5900
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite (T-3)
We recently had to recoat our circa 1984 FB pool. We bought the house in 2013 and the previous owner took many shortcuts in every aspect of the house. Attached is a photo of calcium that could not be sanded off, but had to be sandblasted off before they could apply the new aquaBRIGHT finish. I know that he used CalHypo to chlorinate the pool and there was a leak when we bought the house. I think the calcium was somewhere around 600 when we bought the house but because of the leak, I think it was closer to 1000 for several years. The installer told me that he thinks there will be new recommendations to keep the Calcium lower in FB pools 80-100, but I cannot maintain my CSI at that level. My CH is at 300 and my CSI is -.39
 

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