OK. I’m stumped. Set up a new 110 gal. Freshwater tank a week before Christmas. We reside in upstate NY. Tank filled from well water, which has been softened. GH=50ppm. Tap water pH is about 7.8. A couple of days before adding fish I added a1/2 cup of aquarium salt and 4 oz. of proper pH 7.0. I put in 6 giant danios which all died within 2 days. Then a dozen platys, same results. Australian rainbows, all dead. The blue Gouramis on the other hand did much better. The last one died last night after about a week and a half. Have succeeded in getting ammonia up to 1.0. But no nitrites yet. Copper test shows 0-50 ppm. I’m using 2 Aqua Clear 110 filters and maintaining the tank at 76 deg. Any thoughts? Thanks.