I have a solar collector with copper pipes in it. I would like to use it to heat my fiberglass hot tub. I know chlorine and bromine react with copper and discolor the water. What can I use that will not react with copper? Or is there some way to deal with the result of copper and chlorine?Thanks!

 

It's not a great idea to heat your spa with a copper heater. It will be very important to properly maintain your water chemistry to minimize the amount of copper that gets into the water. Notice I said "minimize" and nothing absolute like "that will prevent the copper from being eroded".

You can also add ozone to your list of things not to use and I think MonoPeroxySulfate (MPS) as well. The core problem is that most sanitizers are oxidizers which can attack copper and many other metals. I think a silver ion treatment (Nature's2) could be used but I have never heard of it being used as the sole sanitizer. Usually it's only used as a maintenance treatment while the heavy lifting is done by an oxidizer.

You could add a heat exchanger so the two waters don't mix. It will add expense and you'll loose efficiency through the exchanger but at least you won't end up with copper blue water.

 

I agree. Use a heat exchanger to isolate the water streams.