Brown Stain on Gunite Pool

by David

I have IRREGULAR, BROWN, RUST-COLORED stains mostly in the SHALLOW END bottom of my GUNITE, salt water pool. What's interesting about the stains are that they are VERY DARK ON THE OUTSIDE of the stains and much lighter on the inside of the stains. Also interesting is that 95% of the stains are IN THE SHALLOW END OF THE POOL.

A lot of them have the shapes parameciums. Some are also U-shaped. The average sizes are only 1/4 inch in diameter. My chlorine levels always run high for the most part. I do get some vegetation in my pool, but less than the average person because most of my trees are far from the pool.

DESPITE KEEPING ORGANIC MATTER OFF THE BOTTOM OF MY POOL, THE STAINS CONTINUE TO FORM. I have balanced my water and tried several metal-out products without success despite following the instructions perfectly. Before I try Ascorbic acid, do the description of these stains ring any bells with you?

I appreciate any your impression of these stains and your recommendations.

Hi David. Most stains such as these are normally either organic or metal stains. First, you can place a tab on an affected area and see if the stain lifts. If it does then it's organic. That's easy to take care of.

Before you do a full AA treatment, you can get
1 lb. of crushed up Vitamin C and put in on another affected area. If the stain lifts or gets lighter, it's probably metal.

Next would be metal stains. There are a few ways metals can get into the water. One is water that contains metals. I would ask if you're on well water? Next would be using copper/metal based algaecides, which you should never use to begin with. The only algaecide to use is a PolyQuat 60.

Then we have rebar bleeding through the plaster. If this is the case, you're going to need to need a professional. That is out of the scope of a quick email.

Through the process of elimination we can say this: No, I'm on city water that has no metals. No, I don't use an algaecide. Then the only other avenue would be rebar.


Thanks Robert

I'm on city water and I have never had to use algaecides. I'll try chlorine tabs on one area and AA on another and let you know results. How would you suggest I apply the AA powder?

Here's a link for an AA treatment:

AA Treatment

The main thing to remember is to add the chlorine back slowly. You're going to use alot of it. In effect, you're starting below zero FC so it will take some chlorine just to get back to zero.

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