Recurring Metal Staining in Fiberglass ( over concrete ) Pool

Jmike_d

New member
Aug 1, 2019
2
Virginia Beach. VA
Been reading a few years, but just joined. First post, hopefully in proper forum location and not too long...

First - this is an old 80's concrete pool that we had resurfaced with fiberglass ( Home ) by a local company back in 2007. For the first 7 or 8 years, we really didn't see any staining at all even though I was not really aware of how to properly monitor and balance the water. I mostly just kept an eye on ph and chlorine with test strips and thew pucks in skimmer as Chl level got low... for all that time, never really saw any staining or other issues.

Then starting about 5 years ago, the stains first started to appear and seem to have been getting progressively worse each year. I've been using sequestrants, sometimes the CULater metal treatment, and Citric Acid to remove and try to prevent since then. I've always figured this was due to iron in the water although we have never filled the pool with ground water. I've just figured the metal has gotten in the water somehow ( maybe rebar in concrete leaching iron? ) and/or the fiberglass surface has become more porous over the years, thus more susceptible to the stains. During the last 3 years I've been using the TF 100 test kit to try stay on top of my water chemistry and be careful not to spike my Chlorine levels with high PH, etc, but to no avail. I can easily get rid of the stains with Citric Acid, but once I bring Chlorine back up, stains return within a day or two.

Part that really confuses me --->>This year I finally got the water tested for metal and the iron level is showing 0.0 with copper around 0.3. The staff has someone who has been in pool industry for 30 years and is typically very knowledgeable, so I generally trust their results. I've had them test the water several times and got the same readings on metal levels.
Is it possible that the stains could actually be something other than iron? would the copper cause brown (rust like ) stains?
Ive kept records since getting TF100, and one thing i've noticed is my Alkalinity this year is considerably higher than in past years ( ~140ish vs ~80ish ) and stains seem much worse this summer. (with it being this high, ph doesn't dip as much as in past ). I've also noticed my Polaris 360 and other plastic white pieces have similar staining this year, which didn't happen previously, so maybe it isn't just the fiberglass aging.

My typical ranges for water this year - TC 1.5, FC 1.0, PH 7.5, ALK 140, Calcium 230, CYA 50 [copper 0.3, iron 0.0 ].

Thanks for anyone who bothered to read this far.
And many thanks to anyone that has any suggestions!

Mike
 

Jmike_d

New member
Aug 1, 2019
2
Virginia Beach. VA
as tested today - TC .23, FC .06, PH 7.3, ALK - 111, Ca 222, CYA 25 [ Copper 0.01, Iron 0.0 ] - I think my copper was .03 rather than .3 previously stated
my PH and Chlorine are lower since I just put some citric acid in yesterday to clear the stains again.

I was talking with the pool guy at store as I was getting my refills for liquid chlorine. He is thinking the staining must be coming from something other than metal. One thing that dawned on me after speaking with him is that about the time we first started seeing the staining, we had someone come and change out the sand in the filter. I think we had him change it out again about 2 years ago. I don't know any details about the sand he used. I haven't been able to reach him lately and never saw what he put in the filter. Just to eliminate it as a possibility, I'll be getting new sand asap.