Alright, I think I slowed the poisoning. I drained my 4x2 150g and filled it with water from my main tank. I filtered the water though a homemade filter using gravel vac tube filled with carbon, with floss on inlet and 100micron pad on the outlet. It took hours to fill the tank through this filter. I also filled a 29g sump with biomedia from main tank as well. I transferred the rays in a large Tupperware container with lid to minimize stress. They are noticeably less stressed now that they reside in the bare 150g. I have not added anything to the water other than prime. Should I add anything? Aquarium salt, stress coat, anything? Now that I can do up to a 50% wc with water from the next town, how large and frequent should I do water changes now?