Rust stains on built in fiberglass steps of IG pool

waterdog

Member
Sep 30, 2007
19
Rochester, NY
I have an 8 year old IG pool with built in fiberglass steps. I've noticed that over the last couple years that round black stains about the size of a dime or a bit smaller, are starting to appear on the steps around the edges where the steps meet the vertical wall of the fiberglass steps. I assume that there is some kind of hardware under the steps, buried under concrete, that are rusting through.

Has anyone experienced this and is there anything I can do to stop this bleed through?

I can post pictures if that would help.

Thanks
 

Butterfly

TFP Expert
LifeTime Supporter
May 30, 2007
10,045
South Carolina
Do you have poor water circulation in that area?

A full set of test results would help us. We need:

FC
CC
TA
CH
CYA


How do you normally chlorinate the pool?

How often do you brush the pool? Does brushing the spots make any difference?
 

waterdog

Member
Sep 30, 2007
19
Rochester, NY
Butterfly,
The pool is an 18k gal vinyl.
Water supply is a good clean muni water supply. I live in the water rich finger lakes/great lakes region.

I'm fairly militant about keeping my chems in check. Although occasionally I might forget and let the CL go to 0.

FC = Typ maintained at 3-5ppm. If I shock I run it up to around 10-15ppm depending on the CYA level.
CC = it's zero every time I check it.
TA = ~70 today (I maintain in the 60-100 range)
PH = 7.6
CH = I haven't checked it in a while but it was on the low side. From what I'v heard this isn't an issue for vinyl. I can test it now if you think it's important.
CYA = right around 30 now.

Virtually all of my CL comes from 12.5% liquid. I use around 10lbs of 3" tablets in the chlorinater per season.

I don't brush often unless I have an algae issue, but I do run an aquabot.

I've tried scrubbing those marks with a magic sponge and it does nothing.

Thanks
 

Butterfly

TFP Expert
LifeTime Supporter
May 30, 2007
10,045
South Carolina
Well, it could be cobalt spotting.

Even tho the vinyl doesn't care about low CH, fiberglass does.

We recommend 220 to 320 CH for a fiberglass pool, and this may be needed for the FG steps.

Let us know how the vitamin C tab works.
 

waterdog

Member
Sep 30, 2007
19
Rochester, NY
Butterfly,
Thanks--- I'll get some vitamin C and give it a try and report back.

I'll also work on boosting the CH based on what you said about fiberglass. Are there less expensive alternatives to boosting CH or is the pool store the only place to get the stuff?

Thanks