Bumps in fiberglass pool

Recently I've seen and felt several (50-60) bumps in the bottom and sides of our fiberglass pool. The bumps range in size from 1" - 3" and are convex shaped. They are really only visibly noticeable in the shaded areas and protrude no more than 1/4" - 1/2" from the sides or bottom. The pool is 12 years old and has never been drained or even lowered below the skimmer. The water chemistry is all in line with ANSI/APSP guidelines.

We've recently had a large amount of rain (Appx 3" - 4") in a very short period of time and am curious if this could be a factor.

Has anyone else here had this occur? Is there anything we can do to get rid of them? And could this be a sign of a greater underlying problem?

Thanks in advance, any comments would be greatly appreciated.

I have no idea about this but just wanted to say hello and welcome you to the Pool Forum. Hopefully, someone will have some advice for you!

Sounds like the gelcoat is blisterng (delaminating). What brand is your fiberglass pool? There was one brand that was prone to this until they changed their gelcoat forumula.

membership upgraded-

It's a Royal Pool sold and installed by Brumett Pools In Clarksville, IN. The bumps have no cracks or fractures in them, just smooth and round.

Royal is one of the older fiberglass companies but they only have a 7 year warranty and do not warranty against blistering, hairline cracking, discoloring, fading, or just about any other pool surface problem! (not really sure what it does cover since there are so many exceptions!) For comparison purposes, San Juan Pools offers a 25 year warranty on theirs.

Sounds like osmotic blistering. This might or might not be a water quality issue. When this occurs on boat hulls it is more likely to happen in fresh water than salt which means it is more likely to happen is water with a lower TDS or in softer water (often these go hand in hand). However, I have only seen very vague references to the cause of this problem in swimming pools. Also, some gelcoat formulations are more prone to blistering than others. My suspicion is that there may be some correlation to low calcium hardness (or TDS) in the pool and the formation of blisters in a gel coat prone to them.