My daughter set up a 55 gallon tank two weeks ago and then last Saturday night, she put 12 tiny goldfish in the tank. I’m not sure what kind of test kit she had bought, but yesterday the ammonia tested in the “Danger” area. I told her she needed to do at least a 50% water change, which she did. After the water change, the ammonia tested in the “Harmful” range. Now this morning, all of the fish are dead except 2 of them. She is absolutely sure it’s because I told her to change at least 50% of the water. Also, she told me this morning that she did not dechlorinate the water when she did the water change last night. When I told her she should have done this, she said the original water she put in the tank a couple of weeks was not dechlorinated either. I’m not sure how the fish managed to live as long as they did in chlorinated water. I’m thinking the fish most likely died as a result of chlorine in the water and high ammonia, NOT the 50% water change that I suggested. Am I right or did I give her really bad advice?