Hi jamulboy and welcome to the forum.
Sorry that no one answered this post or the last one you made, but sometimes the "experts" seem to get busy.
I'm probably not the best individual to reply to this thread, but I'll give it a shot.
Most "composite" materials can be repaired. The "silt" you are seeing is probably from the insulation of the tub "leaking" into the water. The cracks you are speaking of may be "stress" cracks or they could also be caused by a drop or uneven loading of the spa (say filling it on an uneven service).
Sometimes manufacturers have "longer" warranties on their shells, so if you know anything about the tub, I'd suggest you look this up. Also, maybe a few pictures?
Generally, you CAN repair composite shell material. First, turn off and drain the spa. Open the cabinet behind the crack and see what you can see. If the structure is compromised, you may have to re-enforce it with glass. If not, I'd suggest using a roto tool grinding bit to SLIGHTLY increase the width and depth of the cracks, followed by using an epoxy resin to fill them. This product is available at most home stores. It's also a good idea to use a surface tape around the crack to minimize the contact of the epoxy with the shell surface, creating a neater job. Finally, you will need to sand and smooth the repair. You can try and color match with a finishing gelcoat, but this might not be easy for a spa. Realize, no matter what you do, this repair will be OBVIOUSLY visible. Keep that in mind.
Also keep in mind I get my fiberglass and composite experience from working on BOATS, not SPAS. You may want to request additional advice.
Good Luck... post questions if you have them...
Drewski
