Fiberglass pool stains

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C

CKS

Bronze Supporter
Jun 2, 2016
12
Blue Bell, PA
Hi everyone,
I'm starting my 4th year as a pool owner. We bought this house with a 25(?) year old pool. I follow only TFP guidelines and I generally use only 12.5% liquid chlorine to keep my chlorine levels correct. Right now, it's too chilly to swim here near Philadelphia, so I'm using some trichlor tablets in a floater to chlorinate since I need to raise my CYA. Right now, I'm around 20, but I'm keeping my solar cover on 24/7 and running my Pentair controller to regulate my solar panels to warm up the water as much as we can. I'll get some CYA if I need to when it's time to swim if I can't raise it quickly enough with the tablets.

My conundrum is this: we opened the pool this year with virtually no problem except these brown stains where debris had settled over winter. In past years, the sun had cleared these spots over a couple of weeks while we slammed during opening. Not this year. I read the older posts about them possibly being metal stains and trying to use calcium tablets or trichor tablets to try test for certain things, but I couldn't get a clear step by step of what I was trying to test for. I also was confused about when my chlorine had to be at zero and when my pH had to be at certain levels.

Right now, here is where my numbers are:

FC 5
CC 0
CA 50
CYA 20
TA 60
pH 6.8 (just recently dropped and I didn't want to change it today in case it needed to be low for the treatment for the stains).

Thank you so much,
Colleen
 
Coleen, please raise your pH today.... especially with a heater you do *not* want to have low pH running thru copper pipes. That could be the source of stains.

Have you used any copper containing algaecides?

Many times tannin from tree debris will leave a stain if the debris sits too long. A little extra FC over a few weeks should take care of those stains. I'd raise your FC up and brush well often.

Can you post a picture of these stains?

Maddie :flower:
 
Hi, Maddie!
Thanks so much for your quick reply and for the information about the low pH and the copper pipes. We just installed the heater this week and I didn't know about that. The good news is, we haven't even run the heater yet, so that can't be the cause of the stains. The tree debris definitely sat on the bottom of the pool in piles over the winter, and that's where those large brown swatches of stains are. I will post a picture as soon as I can, but it is pouring raining here right now.

How high do you recommend I keep my FC to get rid of those stains? I've been keeping it around 5 ppm with a CYA around 20 or maybe a little less. We'll brush more often too while we raise the CYA.

Thanks so much!
~Colleen

- - - Updated - - -

Sorry - to answer your other question, I have not used any algaecides in the past 2 seasons.
 
Well, it seems like keeping my chlorine up around 8 for another couple of weeks and some additional brushing has not made any difference in the stains. I have some close up pictures of the stains from my underwater camera. Note the close-up of where the worm found its last resting place - sorry wormy. Some stains are in straight lines because it is the settling area at the bottom of the ramp going into the deep end or at the place where the wall meets the floor of the pool. We're pretty certain they're all organic stains - leaf matter and small critter remains. Any suggestions of what to try next?DSCN1778.jpgDSCN1774.jpgDSCN1779.jpgDSCN1779.jpg
 
I have had good luck using vitamin C tablets on these stains. I get the same ones each spring, usually from a worm or leaf that got under the cover, and fell to the bottom during the winter. With a little elbow grease, these stains seem to come up.
 
Colleen, quick question ..... what original color is your shell? Dark blue, light blue, white, green, other? If I didn't know better, I'd think it almost has a chalky/faded look to it. Curious as the pics can be misleading sometimes. As other have suggested, you could try the following:
- Crushed Vitamin C tabs in a thin sock or nylon = iron
- Chlorine tablet (puck) in an area moving around slowly = organic
- Dry acid in a thin sock = copper

With the exception of that one stain that appears to be the outline of a worm (organic), the long consistent stain patterns along the shelves are tough to say. They almost have a brownish look like calcium scale, but your water has been way too acidic for scale to form I would think. I will note however that you should watch the acidity level in the pool. Based on your previous numbers, your CSI level is - 1.49. That's quite low and aggressive. While our FB pools don't have calcium in them to worry about plaster etching, they are still susceptible to various stages of oxidation which can change the gelcoat's appearance. You want your CSI to be close to neutral (zero) or slightly negative (0 to -0.3). Since your CH is so low, the only way to compensate is by increasing both your TA and pH a bit. Using PoolMath, it would take a TA of 80 and pH of 7.6 to get your water out of the "very acidic" range. You would have to increase your CH to 100 for the water to be what we consider "balanced" in PoolMath. Like I said above, even though we don't need calcium to protect plaster, it plays a role in protecting the gelcoat and in some cases stains.
 
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