I just bought a Gulf Coast Spa (Boca) and filled it with my garden hose which takes water from my cistern which is just rain water collected from my roof. Of couse the water looks yucky. Before I fire the tub up what can I do to clarify the water? I'd prefer to try and fix this water instead of draining and filling with city water.

The average cost to fill a tub with city water is around 3 bucks or less, so I would say it is worth the saved headache of dirty water problems to just use the tap. The rainwater wouldn't be bad, but you just introduced bird droppings, leaf residue, bug remains and droppings, chemicals from roofing materials, etc to your spa water...do you really want to soak in all that?