stain/scale on bottom of pool

Hello. Been a reader here for years but this is my first post. I have a tan colored stain/scale on the bottom of my in ground 25,000 gal. vinyl pool. Opened the pool in early June, cleaned up algae and noticed the tan scale. Initial TA was 186. I've since brought that down to 120 and am still lowering. Vaccing and brushing don't seem to help. To the touch the bottom is rough instead of its usual slippery feel. I have noticed that when I bring the pH down to the 7.2 range the water gets brighter and the scale seems to lessen both in visual terms and in terms of touch. When the pH returns to the 7.8 range where my pool seems to level at, the feel and look of the scale returns. Any ideas? Here are my numbers: CYA - 70, TC - 4, FC - 4, pH - 7.2, TA - 120, TH - 198

Hi Bill

Do two things:

1. Try to get a small piece of scale, and put it in a clear glass (like a wine glass). Pour a couple of tablespoons of white vinegar over it. If it fizzes, it's calcium carbonate. If not, leave it overnight, COVERED tightly with Saran wrap. If it dissolves, it's probably STILL calcium carbonate.

2. Meanwhile, read the muriatic acid page linked in my signature, and then use muriatic to lower your pH to near 7.0, and keep it there.

Also, it's much easier to answer your questions, when we have the details about your pool in one place. We often 'waste' the first few posts back and forth collecting information. So, please complete our new Pool Chart form -- it takes about 30 seconds, but will save much more than that.

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Thanks for the reply. I am not able to scrape a piece of the scale off to test with vinegar. The scale does not hold together into anything that I can capture. All of the scale is on the bottom or on the pool side within a few inches of the bottom and it just disintegrates when I scrap at it. I tried to put some vinegar in a glass and then move the glass down the side of the pool to the scale and hold it there. Didn't see any fizzing but it was hard to hold for any length of time and hard to see anything with clarity.

I have lowered the pH and am holding at 7.

With the pH at, or just below, pH 7, any calcium scale should weaken and maybe disappear in a few days.

Thanks, I'll let you know if it works. A neighbor gave me something called Metal Magic that he said would work. I'm keeping it as a last resort. I'm reluctant to put anything in the pool that I'm unsure of. Have you heard of this product and its effectiveness in removing calcium scaling?

Unless that product does something that I'm not aware of, it isn't going to help your situation. Metal sequestering agents keep metals in suspension instead of staining pools. Yours is a different problem. Don't add it unless Ben tells you to do so.