Plaster Stain

[jamfitz]

Hi...

Purchased a home with an old pool in horrible shape. Last year I had the old surface sand-blasted/replastered with a smooth white plaster finish. I just opened the pool, and the walls and the shallow area pool bottom have a blotchy greenish stain on them. I've tried brushing it off but that's not working. What type of stain might it be and how to I deal with it?

Thanks!

JF

[Woodsy]

I just had a guy in the store today with about the same description. Where's waterbear? I couldn't think of a mineral that would appear green. This guy's water chemistry was pretty good as well. His pH was a little on the high side, but that was it.

[waterbear]

Where's waterbear?

"There's no need to fear, Waterbear is here!" (Sorry, just couldn't help ripping off 'Underdog!'

Seriously, copper can cause bluish green stains. If they are bright green I suspect they are algae. Without posting a full set of test results it's just a shot in the dark but you can try a few things.

Hold a trichlor tablet on the stains. If they lighten or go away they are organic or algae. Shocking and brushing will get rid of it. What is the FC and CYA levels in the water? If they turn grey or black they are copper.

Try holding a vitamin C tablet on the stain. If they disappear in a minute or less they are an easily removed form of copper. Not all forms of copper staining respond to ascorbic acid (vitamin C)

Put some dry acid in a gym sock and hold it on the stain for about 20 minutes with your pole. If they disappear they are metal and an acid wash will remove them. You might be successful with a no drain acid wash procedure if the staining is not too bad.

I have a feeling they are algae embedded in the plaster. You did not say whether you used a nylon, SS or combo brush. For plaster you might need a combo or SS brush to get algae off of it.

High pH conditions are what ususally lead to staining or scaling.