Is that a Blister? - Fiberglass Pool

[HBrittan]

Good Morning,
I started cleaning some spots and fine tuning details after a major SLAM and clean up job. Upon further inspection, I noticed that these black spots wer not stains as I thought but rather seem to be blisters in the pool surface. This is on the top step of an older fiberglass pool. Not sure how it happened, if something was dropped, chemicals, or whatever.

Here is a picture. Is about 4-6 inches under water on the top step. These are the only spots like this that I have seen in the entire pool, and I have checked it pretty well.



My questions - What might have caused this (if not impact), and is there anything I can do to repair it?

Thanks,
Harry

 

[Texas Splash]

My questions - What might have caused this (if not impact), and is there anything I can do to repair it?

Unfortunately, no way for us to know Harry. A FB pool can get small chips or blemishes in the gelcoat, but those seem odd because they are also discolored, unless the entire shell is dark underneath. Maybe something fell on the step, maybe something pushed "upwards" from below? Being an older FG pool, I suspect the shell was fabricated with different products than today's pools, so previous chemical care would be important.

Moving forward though, a good pool or marine FB repair shop should be able to take care of those for you. Because the pool is old, I would maintain a decent CH level as well since calcium may be a byproduct of its fabrication. I would keep the CH around 300-350 minimum. Hope that helps.

 

[sktn77a]

Doesn't look like typical blistering. Usually, you'd have a raised bump there for a few years before they physically cracked/chipped like that. You can get gelcoat repair stuff but you need to drain the pool below the step level and make sure the fiberglass substrate is thoroughly dry.

 

[HBrittan]

Texas Spalsh and sktn77a, Thank you for the feedback. I should have put something next to the spots to give some idea about he size. They are really pretty small. Maybe about a 1/4 in or so. Glad to hear it is not blisttered. I am not really sure what that would look like. I am betting something hit it and chipped it but can’t really know. The water was nearly black when we started to SLAM our pool in May that had been closed for nearly 18 months. I can only imagine that maybe that discolored it.

I will look at patching/repair options, and go from there.

I am also betting that the CH was low for a really long time.. I just increased it from 200 to 400 CH and will continue to test that on occasion and maintain it.

Thanks again. Have a great weekend.
H