FG Pool 'dirt' Stains?

[revitup]

New FG pool last fall. My water is clear as gin. The chems have been dialed in for weeks now. The problem is that I’m seeing what looks like tan colored ‘dirt’ stains on the bottom in a couple areas that seem to always collect organic debris. A large part of the walking ledge also looks dirty to me. Seems to be the anti-skid surface that’s dirty. Hard to see in the photos.

Tried putting chlorine tabs on the areas, did not seem to have any effect. Brushing with a nylon bristle pool brush has no effect. A red/maroon Scotch-Brite pad at least lightened it up. Could any of this just be the result of not brushing the pool (ever, until recently)? Seems like I’d need a pretty aggressive brush to get this off and keep it off. Any suggestions for dealing with this?

 

[Texas Splash]

Rev, it's tough to see in the pic, but I don't have a good explanation for your discoloration issue at the moment. Can you do the following:
- Post a full set of water test results? Let us know if there have been any wide swings in chemistry over the months.
- Let us know if you have added any other chemicals to the water other than the standard stuff (salt, maybe chlorine, acid, baking soda, etc).
- Any flooding or history of stuff that could've been washed into the pool?

Let's start there and see what we come-up with.

 

[duraleigh]

Crush up a bunch of cheap Vitamin C tabs (maybe 20) and put them in a sock. Place the sock directly onto the stains and weight it down with a small brick or something like that.

Let the crushed Vitamin C tabs (ascorbic acid) remain on the stain for maybe 2-3 minutes. If the stain is removed, it is iron depositing on your surface

 

[revitup]

I know it’s tough to see the discoloration in the photos. I feel kinda bad even mentioning this issue with all the serious problems I see others having with their pools. The levels have been very stable, been chasing TC a bit, playing with SCG output level trying to get that dialed in too. Never falling below minimum TC.

Maintained the pool all off season and so opened to a clear pool. I’ve added little since we opened. Nothing exotic, nothing that isn’t on the TFP recommended list. No wide swings in chemistry, brought TA up a little recently with a few acid additions. Brought CH up from 270 to 350.

All my tests and adjustments are documented in my PoolMath Logs. Here’s a set I just took this morning. Got 1” of rain couple days ago. Nothing out of character for the pool:

TC 9.5

CC 0

PH 7.7

TA 70

CH 360

CYA 60

SALT 3200

TEMP 87

CSI -.06

No flooding or anything washing into the pool. We have quite a few trees around and they just finished their spring pollen/leaf/seed dump a couple of weeks ago. As I mentioned, there are a couple of areas on the pool bottom where this debris seems to congregate and that’s where the bottom stains are. I can just vac those small areas and have the bottom 95% clean.

Can’t explain why the anti-skid surface on the walking ledge looks so dingy in areas. We hardly use it.

Did the vitamin C test in both locations, the bottom stain and the walking ledge discoloration. It had no effect.

 

[Texas Splash]

Can’t explain why the anti-skid surface on the walking ledge looks so dingy in areas. We hardly use it.

Your test numbers look good right now, and you ruled-out iron and organics. If you just opened though, the pH might have been higher for the last 3-4 months and perhaps the discoloration is slight scale. It's a bit of a stretch, but it's the only thing that seems somewhat possible, especially if you rarely brushed some areas in the past. You might make a conscious effort to keep the CSI slightly negative as you have it right now, maybe even -0.1 to -0.3 for a few weeks. Brush 2-3 times a day in those troubled areas, or at least in one of those areas, to see if it gets any better.

 

[revitup]

If you just opened though, the pH might have been higher for the last 3-4 months and perhaps the discoloration is slight scale.

The pool was actively maintained during the off season, PH kept 7-5 - 7.9.
I'd like to find some method to more quickly remove the existing stains. Is red/maroon Scotch-Brite safe to use on gelcoat? The typical plastic bristle pool brush doesn't work. Is there a more aggressive brush type that's still safe for use on fiberglass?

 

[Texas Splash]

Is red/maroon Scotch-Brite safe to use on gelcoat? The typical plastic bristle pool brush doesn't work. Is there a more aggressive brush type that's still safe for use on fiberglass?

I have found that for my issues, brushes don't do anything if something is embedded in the top layer of the gelcoat. I have used various wet sandpapers (the black paper) on my gelcoat. Try using a 1000 grit first and work your way down if you need to. If you end-up using something more rough than 400, it might leave some very small, superficial scratches, but they are so small you shouldn't really see them unless you have your eyes right up against it. But try a small area first to see if you are pleased with the results.

 

[duraleigh]

I am curious, Pat, does the 400 grit sorta dull the finish or is the finish not high gloss enough to show?

 

[Texas Splash]

I am curious, Pat, does the 400 grit sorta dull the finish or is the finish not high gloss enough to show?

Very fine grit has a minimal effect on the gloss, especially when underwater. Using wet/dry was something suggested by my installer when I had a similar issue.

 

[duraleigh]

Thanks!

 

[revitup]

I'm still trying to determine what this staining is in our FG pool, or if it is a stain, for that matter. It's hard to see in the photos but the stain appears to be almost exclusively on the walls of the pool with very little on the floor, walking ledge and seats. Others who have seen it say it may be a natural discoloration of the gelcoat or that there's nothing there at all!
I bought a Jack's Stain ID Kit with the intent of making one last attempt to ID the stain. The problem I'm having is figuring out a way to hold the packets from the ID kit in place on a vertical wall long enough to show some result. Trying not to over-engineer this. Anyone have any ideas of how to hold the packets on a vertical surface?