Bumps in fiberglass pool

[mister59]

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.

[waterbear]

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.