"mark Bannister" wrote
I'm pretty sure nothing can "sink into" fiberglass.


Au contraire, Monsieur. As any boat owner will tell you, the fiberglass
plies are coated with "gel coat", an outer layer of resin not containing any
fibers. This protective layer works pretty well, but breaks down in sunlight
over time, and it can be damaged/scratched by hard objects. Holes in the
fiberglass (as for jets) are usually unprotected by gel as well. I would
imagine that an older tub has lots of wear and more than a few avenues for
"stuff" to get into the layers of fiberglass below the gel.

OTOH, I doubt that the stuff put into a hot tub over the years is likely to
be harmful to the fish. A good non-abrasive scrubing should remove any
surface contaminants. And if there remains some concern, line the tub with
pond liner (difficult and unattractive) or paint a layer of clear gel inside
yourself (easy and not a lot of work). Boat owneres do it all the time and
you can get some at most any boat supply retailer.


Michael
New Orleans, Louisiana USA
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