Does High Alkalinity destroy Vinyl Liner?

[fhaley]

I have an Inground Vinyl liner pool that has, what appears to be dry rot just above the water line in one corner. When I talked to the liner installer/pool store, He said that high alkalinity will cause this. I know my fill water is high alkalinity, so I was wondering if he is right. I have no scaling or anything, so I haven't been to proactive to keep it down. The liner is about 5 years old, and will have to be replaced this year or next spring at the latest. I don't want to be doing something that will continue to degrade my liner so fast. It seems I can only get 3-5
years out of a liner. When I replace this liner it will be the 4th liner since pool was built in Spring 2000.

[chem geek]

Welcome to The PoolForum!

I don't think that a high Total Alkalinity (TA) level has anything to do with dry rot above the water line, especially if you aren't seeing any scale forming. I could imagine that a combination of high pH, TA and Calcium Hardness (CH) might lead to some scale forming above the water line due to wetting/evaporation cycles and maybe such a film can lead to a problem with the vinyl underneath.

Are you using Trichlor pucks/tabs in a floating feeder? If so, does it tend to park itself in the corner where there is a dry rot problem? The acidity from the Trichlor tablets will not be good for vinyl so if the floater tends to park itself in one place, then when the pump is off and there is no circulation the acidity can lower the pH substantially locally and cause problems.

If you are using chlorinating liquid or bleach as your primary source of chlorine, then a high TA level will often result in the pH getting too high. Do you have a Taylor K-2006 test kit? If not, get it here. Then post your full set of water chemistry numbers:

Free Chlorine (FC)
Combined Chlorine (CC)
pH
Total Alkalinity (TA)
Calcium Hardness (CH)
Cyanuric Acid (CYA)

Also let us know your water temperature and more details about your pool. What size is it? What kind of filter do you have (cartridge, sand, DE)? What kind of chlorine are you using and what other chemicals are you adding to your pool?