Light yellow streaks in low end on vinyl pool liner

by Peter

I have a 28,000 gallon in ground pool with vinyl liner, using a nautilus DE filter, about 30 years old. The pool is a swamp every year when I open it, due to the looplock pool cover. It takes a bit of cleaning, but I am always able to get it perfect after about 2 weeks. This year, the water looks fine and the chlorine levels and PH are within normal range. According to pool store tests, everything else was in normal range as well with no significant metals. My CYA was at a 90, but I was told this is okay. The problem I'm having is that there are light yellow streaks on the bottom of the pool in the low end. The stains are mostly in line with the jets on both sides of the pool. The stain begins about 2.5 feet in front of the jets and ends at the slope to the deep end. I believe it's a chemical stain, but don't know for sure. I added "green to clean" and 2lbs of granular shock directly to the pool, but I've done this in the past and never had this problem. I also assumed the stain would be white if it was from the granular shock. The other things I added were alkalinity up, 30lbs twice about 3 weeks apart. I added this directly to the pool, again as I've done in the past. And finally, I added 10lbs of soda ash, but mixed with water first. This I haven't done in the past. It was clumpy when I added to the pool. If it's

a chemical stain I'm wondering if it was from the soda ash. Please let me know what you think is the cause and if there is anything I can do to remove it.

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Hi Peter. 90% of the time stains can be chemical, organic, or metals. The way to test is to place a chlorine tab on an affected area for a couple of minutes. If the stain gets lighter it's organic and can be treated by shocking the pool.

If the stain doesn't lift or gets darker, then crush up 1/2 lb. of vitamin C tablets, place it in a sock and put it on the stain. If it gets lighter, it's metals. The question doesn't state whether the pool water has metals.

The other is a chemical stain. This is when chlorine or acid is added to the pool in one area and is allowed to settle to the bottom. There's not much that can be done for it. It's like pouring bleach in your jeans.

The last area could be bacteria or mold leaching from under the liner. The only way to stop it is to remove the liner, fix the mold and/or leak, and replace the liner.

Soda ash is pretty benign and shouldn't cause a localized stain. TA Up is sodium bicarb and is very safe for liners.

A DE filter wouldn't cause localized stain either. It sounds like you've had the pool for many years, so I can safely assume you know what you're doing in terms of balancing the water and maintaining the filter.

Good luck and have a great day.

Robert