White deposits on my Fiberglass pool


New member
Sep 2, 2021
sydney aus
Moved from here... White deposits covering Fiberglass pool

Hi all

I thought Id update this thread given others mentioned they had similar issues.

I drained the pool and took photos of what it looked like with no water.

Undiluted hydrochloric acid did not touch the staining so I guess it was chlorine etching the gelcoat.




I ended up sanding the entire surface and buffing with a rotary:


Hi SBV, I have what i think is exactly the same problem as you, i also have never owned a pool before and feel totally abandoned by the all the companies involved in my sale from the on seller to the equipment suppliers. I have done the pool stain removers treatment and nothing.
my pool is 3 yrs old and i have a hayward chromatalyzer and chlorinator fitted to the system. i also have water tests done by pool shops with centrifugal testing machines and not strips usually every 2 weeks. (i have missed a few)
My problem is, i have this whitish stain, it has no texture, its smooth, and i notice it most on the vertical walls of the pool, it doesn't seem to effect the bends of the fibre glass which appear darker in colour. i also have some sort of water droplet effect like as when you'd wash a car and leave the water droplets to dry and then they penetrate into the paint work.

i have recently discovered that my chromatylyzer (machine that regulates the chlorinator and does auto acid feed (regulates free chlorine and PH)
has not been doing its job properly as it was not calibrated properly after the manufacturer came out and replaced some parts they calibrated it using the pool water which was out and not raw water ( i cant prove this as i have no paper trail from them mentioning a recalibration but they told me verbally.) so the machine was thinking the pool water which was balanced was 0 point so it doubled the actuall levels. for almost 2 years i had high free and combined chlorine at about 5.5-6.5ppm (free). i am of the belief i have chlorine bleaching. rather than calcium silicate issues.

I also tried 1500 wet and dry sand paper and it took a lot of effort to remove 85% of the staining on that spot.
I cant access your photos so i cant see how yours looks now or during the repair stage.
i have more photos i can share. Just so everyone knows i'm very fussy with my upkeeping and not having a knowledge good enough to argue, the pool shop kept making excuses and reassuring me the chlorine levels were off due to alot of different other things and they would come good and not to worry. as levels can change very quickly
cheers John


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Gold Supporter
LifeTime Supporter
TFP Guide
Jul 3, 2013
Southern OK
Pool Size
Salt Water Generator
SWG Type
CircuPool SJ-40
Welcome to TFP :)

Free Chlorine of 6 is not high if you also have CYA... I keep my CYA at 80 and FC at 7 at all times... Do you have your own test kit or do you rely on the pool store testing?
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