Rust in fiberglass crack - how to remove?

marthas_ear

LifeTime Supporter
Mar 7, 2009
67
Texas (Central)
How can I remove a 5 inch vertical rust stain in fiberglass side of pool?
I tried Magic Eraser and bleach. We figure it is coming from the rebar under the concrete decking.
Crack doesn't seem to be other than surface.
We also have hard water and you can see we also have a problem with calcium build up at the water line.
Would like suggestions for that clean up too. It's hard as a rock. ;-)
 

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Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Allen gave you the Vitamin C method. Interesting that the shell has what appears to be a stress crack, but the decking above looks fine. Were you the original pool installers, or was it there before you moved in? As for the scale, it's no easy DIY chore. First, confirm it's actually calcium scale. Apply a small amount of undiluted muriatic acid directly to an area. You should see a reaction (fizzling). If you do, you might try carefully spraying muriatic acid directly on that waterline. Experiment with diluting a bit first. careful scrubbing may help, but you have to be very careful with wind direction and overspray on hands, eyes, hands, arms, etc. Some might try to keep the waterline level elevated and maintain a negative CSI for several weeks with daily scrubbing in an effort to try and thin it out. For plaster pools, some people with have a type of sand blasting done. I've not heard about it done on FG, but if you contact a service provider they should be able to tell if you if it's possible and/or any potential side effects.
 

marthas_ear

LifeTime Supporter
Mar 7, 2009
67
Texas (Central)
Thanks! Haven't tried Ascorbic Acid yet. Sounds like a plan.
We had the pool installed. My husband watched them install it. It's a stress crack. He also had success with muriatic acid removing the scale. Good to know we are on the right track.
 
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Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
He also had success with muriatic acid removing the scale.
Great. So once you two finish treating the visible waterline scale, you'll want to make sure to do the following to prevent it from returning:
- Use our PoolMath APP to ensure your CSI is always slightly negative. CSI is controlled by four factors - water temp, CH, TA, and pH. PH has the most immediate and radical impact on CSI, so make sure to control it with muriatic acid if it gets over 7.8.
- Make sure you are chlorinating with liquid pool chlorine or regular bleach - same thing just different strengths.
- If your local water is hard, never use Cal-Hypo powdered chlorine. More calcium is the last thing you need.

Let us know if you have any other questions.