Dirt, Rust Stains, and Clumps on bottom of gunite pool


LifeTime Supporter
Jun 7, 2008
Cincinnati, OH
Good day everyone,

Newbie here, great site, very informative. :-D

We purchased a foreclosed home, empty for 3 years and it was a mess, so bad, we could not see the top step into the pool and had no idea which end was shallow and deep. We had the pool professionally dumped and cleaned (acid washed) and it did a very good job of getting our pool back. After this was done we needed to have all tiles replaced and the contractors got the bottom of the pool dirty. I was able to pressure wash the shallow end (which had no water in it) however the deep end was not completely drained and I have these stains that look like dirt. Also, I have noticed that we have a few 4-5 long straight stains that appear to be rust colored. The stains are about 3-4 inches long and almost look like a nail was on the bottom of the pool for a while, but there was no nail in that spot.

What is the best way to clean these stains, I have brushed the areas (like mad) and I don't make any progress. I really don't want to empty and acid wash again if I don't need to.

Also, it appears the tile contractors dropped grout or thinset which has adhered to the bottom of the pool, some in the deep end, some in the shallow end. The strange thing is I don't recall this clump being in the shallow end when I pressure washed. Could these be hard water deposits or calcium buildups? What is the best method to remove these clumps , I was thinkings a flat head screwdriver or putty knife, however I don't want to ruin the gunite.

Thank in advance for your help.


TFP Expert
LifeTime Supporter
In The Industry
May 20, 2007
SWSuburban Chicago, IL
I can't help with the gunite issues, I know zero about that.

As for stains, if they are metal, you rub absorbic acid or Vitamin C tablets on th stain and if they go away they are metal and you follow these instructions: http://www.troublefreepool.com/sticky.php?s=2298

If they aren't metal you rub a chlorine tablet (got any pucks-dichlor or trichlor?) or maybe not rub, put in a sock and let the puck sit on the stain and if they fade they are an algea stain, can can be treated by bleach.


Don't rub in either case. Hold a vitamin C tablet on the stain for about 30 seconds. If it lifts the stain then ascorbic acid will work. If it doesn't put some pH down in a sock and hold it on the stain for about 30 minues. If this lifts the stain then you need to acid wash. There are no drain acid wash kits available, btw. If this doesn't work hold a trichlor tablet on the stain for about 20-30 minutes. If it lightens then it's organic and very high FC levels will eventually lighten them.