Hi, Mark,

There's not too many fibreglas owners on the forum here so you may have to be patient. (I'm not one)

Did you use PVC on both the boiler and pool side of your exchanger? If so, what temp is your boiler water coming into the exchanger? I'm thinking I'll probably use brass and PEX on the hot side and PVC on the pool side.

Since the metal precipitated out onto your fibreglas and you have eliminated the source, I don't think you'll have any further problems

Is your exchanger copper or stainless? If it's copper (on the inside), faulty pH can eat up the copper pipes pretty quickly. Stainless is pretty bullet proof but can still have some fittings that are just black iron that can lead to issues like you've experienced.

Dave S.