Large, black stain on pool floor after opening!


Well-known member
May 29, 2017
Worcester, MA
Hi folks:

We opened up our pool today. 32K gallon Gunite, inground.

I was pleased to see the water was pretty clear when we pulled back the LoopLock cover. Much much much cleaner than the green swamp we had last year when we opened!

Overall the pool looks great and I've started my SLAM. EXCEPT...there is a large, dark / blackish stain on the floor adjacent to my floor drain. It looks as if something (leaves, other debris) was stuck there over winter. The debris is gone but the stain is unsightly.

I've tried scrubbing in for minutes with my plastic brush on the end of the pole. I've driven my Dolphin M500 robot back and forth over it a dozen times. It seems a "bit" better but is still there.

Suggestions on how to get rid of it without having to drain the pool? Pool chemistry is ok. PH is too high, and CH a tiny bit low. Otherwise all is good.


Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
If it's organic from leaves as you suspect, maintaining the FC slightly higher than normal for your current CYA should help them disappear. You can confirm by setting a chlorine tablet on that area for a minute or two, maybe move it around slightly as it's acidic. But if you see a reaction to the tab, you know it's organic and you just need to give the chlorine time to work on the stain. Continue the brushing each day as well. :)