Nicole, I understand you're doing all you can for the fishes left in your care. Perhaps instead of another tank you could invest in a top of the line filtration system to keep their water in better shape. I know that the pet stores here will test a water sample for you and could assist you with keeping it in the best shape you can. Another tank is just going to be so much more work. It's going to be a few months yet before a pond can be dug and set up so do what you can dear. Get a book or two or perhaps read on the "net" about what you can do for them in the short term.