Hi all,
I'm starting a new hot tub after we got rid of the old one more than a year ago. I do have basic understanding of water chemistry, but I'd still consider myself a beginner. I'm trying to understand what could I have done wrong to end up with white deposit on our brand new FG pool after less than three weeks. I don't think it's anything to do with the pool itself as the deposit is actually worse on the non-FG plastic bits.
After having built up CYA using dichlor I switched to a very old bottle of liquid chlorine, which seemed to be down to 2% active. After a week, when pH went through the roof, I switched to a new bottle of 12.5% liquid chlorine.
The tub is an above ground dual spa + swim spa. The affected spa part is around 1500 L (400 gal) kept at 35C (95F). The larger swim spa part's water is maintained separately and to slightly different targets, and shows no signs of damage.
Attached is my full log and photos of damage. Target values are included in the first line of the log. Values in parentheses are not actual measurements, usually just carried over or calculated. I'm using the Taylor K-2006 test kit.
The deposit doesn't feel different to the touch from other parts of the pool. It's not coming off with a sponge. I applied muriatic acid to the back of the plastic cover and that seems to have helped, but I'm afraid to go ahead with the acid on the FG in case I cause more damage.
Thank you!
I'm starting a new hot tub after we got rid of the old one more than a year ago. I do have basic understanding of water chemistry, but I'd still consider myself a beginner. I'm trying to understand what could I have done wrong to end up with white deposit on our brand new FG pool after less than three weeks. I don't think it's anything to do with the pool itself as the deposit is actually worse on the non-FG plastic bits.
After having built up CYA using dichlor I switched to a very old bottle of liquid chlorine, which seemed to be down to 2% active. After a week, when pH went through the roof, I switched to a new bottle of 12.5% liquid chlorine.
The tub is an above ground dual spa + swim spa. The affected spa part is around 1500 L (400 gal) kept at 35C (95F). The larger swim spa part's water is maintained separately and to slightly different targets, and shows no signs of damage.
Attached is my full log and photos of damage. Target values are included in the first line of the log. Values in parentheses are not actual measurements, usually just carried over or calculated. I'm using the Taylor K-2006 test kit.
The deposit doesn't feel different to the touch from other parts of the pool. It's not coming off with a sponge. I applied muriatic acid to the back of the plastic cover and that seems to have helped, but I'm afraid to go ahead with the acid on the FG in case I cause more damage.
Thank you!
Attachments
Last edited:
Touch call really. We have found by surveying many TFP fiberglass pool owners that gelcoat changes can/do happen, but there doesn't appear to be a common denominator at this point. Older pools seem to be more susceptible to fading/chalkiness, but I don't think yours is in that category. Your test values seem fine overall. There may have been a period early on where the TA was a bit low. Some FG owners experienced chalkiness with a low TA, but in their cases the substance wiped off. Yours seems embedded. In those cases we watch to see if there was an oxidation reaction due to an excessive FC combined with an elevated pH perhaps. You had a few places here & there where the numbers were a little out of range, but nothing that would indicate a pattern of poor chemistry long enough to explain the changes you are seeing.
Nothing stands out to me that would explain the changes you are experiencing. I wish I had more info to provide.
