Discoloration of gelcoat after SLAM

[jollyjeff]

I have a 2 year old fiberglass pool that so far has been very easy to care for, owed largely in part to the info that I've learned on TFP.

This Spring, I had my first encounter with mustard algae. I normally keep all of my chemicals balanced using a Taylor K2006 kit. However, we went on a 3 day vacation in May and some sudden increased temps overran what I had my iChlor 30 SWG set for. This seemed to have caused my FC to drop to levels that allowed mustard algae to set in.

I immediately followed the SLAM method after returning home, which required me to raise my FC to 28ppm, given that my CYA was at 70. I did this using liquid chlorine, frequent brushing and backwashing of my sand filter, and was able to eliminate the mustard algae while letting it drift back down over the course of about 3 - 4 days.

Yesterday, while cleaning the pool, I noticed what appeared to be some discoloration in spots of the gelcoat on the bottom of the pool. It was most noticeable at dusk. I brushed the areas, but it did not appear to be collection of dirt, or anything loose on the bottom. It isn't a huge deal, but I tend to be OCD and get fixated on things if I feel that there is something wrong. It appears to be areas where the blue is brighter than others, but it's so subtle that I would probably be the only one that ever notices it. However, I was concerned that the high levels of FC might have caused some bleaching, or if it could be some sort of metals that have stained the bottom in the SLAM process. I've never used anything other than liquid chlorine, baking soda, muriatic acid, calcium chloride, and stabilizer.

I've included pics, but it's very difficult to see the color differences in them.

Here are the readings from my latest K2006 test:
PH - 7.4
FC - 6.5
CC - 0.2
CH - 280
TA - 80
CYA - 60
Salinity - 3500

Thanks

 

[Texas Splash]

I was concerned that the high levels of FC might have caused some bleaching,

I doubt it. While some pool manufactures might claim otherwise (extreme oxidization), the science behind TFP levels and FC-to-CYA ratios doesn't support it, at least not for a short period of time. What we have seen on the forum, myself included, is that some gelcoats simply start to transition from the original/pristine color to a faded/chalky look over time. Not all pools do it, but many of them do, and there is no apparent rhyme or reason. In my case it started around year three I believe. It's mostly noticeable if you lower the water level down a bit. Nothing that could be done. Even if I sanded an area down back to the original dark blue, the area reverted back to the chalky appearance in the next season or two. Gelcoats are porous on a micro level and we expect they will change over time regardless of the chemistry.

 

[jollyjeff]

I was looking this morning when the sun came out and it's barely noticeable in the sunlight. I wonder if it could simply be where the textured surface on the pool bottom was applied slightly heavier in places during manufacturing, and is now more visible than before in low sunlight. It did make me feel better that it wasn't visible in good sunlight.

I felt like if it were some sort of bleaching, the walls, tanning ledge, and steps would be discolored as well, but they aren't.

I'm not gonna lie.. getting chloring up to 28 ppm did make me cringe a little after reading manufacturer warnings that state to not exceed 5 ppm

 

[Texas Splash]

I felt like if it were some sort of bleaching, the walls, tanning ledge, and steps would be discolored as well, but they aren't.

That's good then. I agree, if it was something related to the quality of the gel batch you would probably see more widespread indications.