I'm not exactly new to keeping fish, but I would consider myself a beginner I am having trouble with my newest tank set up. I will describe my conditions as best I can but I would greatly appreciate some advice. I recently had several ghost shrimp, three mollies and a dwarf gourami in a 10 gallon tank for quite a while. Suddenly, my gourami died and so did one of my mollies. Sensing something was wrong, I quickly did a water change (thinking that it could be an ammonia spike). While I was changing the water, I realized that the gravel was full of muck underneath. It was probably making the water disgusting. I recently came upon a larger tank. I think it's a 20 gallon tall [photo included]. I covered the bottom in pool filter sand, put in some of the water from the old 10 gallon, moved the filter to the new tank and filled it up the rest of the way. I conditioned the water, of course. There is a little bit if aquarium salt in the water as well. I now have a very small 1/2" green spotted puffer from Wal-Mart. I know that Walmart sells sick fish sometimes, but all of his tank mates were starving to death and I wanted him to have at least some chance at life. There is also a Wal-Mart violet goby in this tank. I plan on slowly changing the water to brackish after the puffer puts on some weight. As of yesterday, the mollies were visibly shimmying. My research says that this is a symptom of bad water quality. My puffer has been swimming the walls of his tank. He doesn't look frantic, but he has not eaten any frozen bloodworms today, like he was yesterday. In light of this, I went to Wal-Mart again and got test strips, along with Tetra SafeStart. The strips revealed that my nitrate and nitrite levels are safe, my water is soft, the alkalinity is "high" and my pH is.... 8.4! Alkaline! So I added the entire bottle of SafeStart to boost the ammonia eating bacteria in the tank. I figured that wasn't going to help the pH though, so I went back to Wal-Mart and got Tetra Easy Balance. I medicated the tank and waited a few hours. My black Molly is still visibly thrashing. The other two do it occasionally, but he is by far the most sensitive. Does anybody have further advice for me? I could really use it as I've never had a fish as advanced as a Puffer or Goby before. I am afraid that I might tip the water to the point of no return if I overfeed them bloodworms even a little bit.