Gunite/plaster stains

Matt 633

LifeTime Supporter
Jul 27, 2007
40
Western East Texas
I am currently helping a friend that has let their pool get away from them. Over this last weeked, they drained and refilled their 25K gallon pool. I have been able to help and advise them about the water and it is now under control. The bottom of the pool is very stained - looks dirty. Does anyone have any suggestions other than a complete drain and acid washing? I realize that acid washing is probably better left up to the pros, but we're pretty hands on people that wouldn't mind tackling this.

Thoughts please!
 

JasonLion

TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
37,879
Silver Spring, MD
The first thing to do is to figure out what kind of stains they are. Try lightly rubbing with some crushed Vitamin C tablets in a sock and with a trichlor tablet and tell us what happens. Vitamin C will remove metal stains and trichlor will remove organic stains. If neither works it is probably scale, though there are a couple of other possibilities.
 

Matt 633

LifeTime Supporter
Jul 27, 2007
40
Western East Texas
Many thanks Jason. It isn't metal staining - though there are a few spots in the pool where iron staining is appearant - rusty appearance- looks like something fell to the bottom and started to decompose.

My guess would be organic. It looks like there may have been a solids (algae?) build up at one point and it has left some type of staining after draining. Much like a very bad bath tub ring. The sides look the worst.

I'll try the tri-clor puck this weekend.

Again, many thanks.
 

Matt 633

LifeTime Supporter
Jul 27, 2007
40
Western East Texas
The staining is organic in nature. Tri-chlor will dissolve it pretty well. Upon further evaluation, I would imagine that a good scrubbing and power wash would bring it back to life. Short of draining and doing this, what's the suggested course of action?
 

JasonLion

TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
37,879
Silver Spring, MD
Bring the pool up to shock level and brush the stained areas several times a day while holding it at shock level. In most cases a day or two of this will take care of the staining. Shock level depends on the CYA level, 12 to 15 with CYA around 25.

If it is actually black algae the stains will usually return unless FC is held at the high end of the normal range, around 6 for CYA of 25. Hopefully it is something else.