Vitamin c tablet left dark stain- help


New member
May 1, 2018
Pensacola fl
Hello- have 18500 gunite pool. I had some brown staining on steps, so tried a vitamin c tablet and worked great. So I dropped a couple on steps and went to do other stuff and forgot about them. The filter turned off and in am I noticed a dark brown/black stain where tablet was. I tried scrubbing and will not come off. Worried it oxidized or burnt gunite. I am wondering if could be scrubbed out with pumice stone or acid direct on spot. Do not want to create additional problem. Water is clear and chemicals balanced- FC was around 1ppm- slowly raising. Any thoughts.

Texas Splash

Mod Squad
LifeTime Supporter
TFP Expert
Hello and welcome to TFP! :wave: Do you have any dry acid? You might try a little of that in a sock or something and hold it there for a minute or so to see if that changes anything. When you do report back, it would be helpful to have the following info:
- Which test kit you use
- Full set of results (FC, CC, CYA, PH, TA, CH)
- How do you chlorinate your pool?
- Any other items that have been added to the water in the past 12 months or so (pool store products, algaecides, anything).

We'll start there and see what we can do to help. Nice to have you with us from P-Cola. I'm at Randolph. :wink: