Hi all, I'm new at keeping fish and have been trying to read all I can to learn about proper aquarium care. A few months ago I bought a 2.5 gallon tank and 1 long-finned zebra danio. After a month I bought 1 glofish danio. Then I read about how danios are schooling fish and should be in a bigger tank with 5-6 in school. I bought a 15 gallon tank about a month ago. When I set up the new tank I used API stress zone plus as directed on the bottle. After 30 hours I transferred the 2 danios to the 15 gallon tank. Boy, did they look happy happy happy. After about a week I went and got some friends for them. 3 long-finned leopard danios and a short-finned zebra danio. 2 days later one of the leopard danios was dead, stuck between the filter and the aquarium. Other than that, the fish seemed pretty happy...if anything the glofish looked like he was being left out of the fun a little bit. A few weeks went by. Last week the glofish wasn't looking too hot. His blue color faded and he hovered on one side of the tank struggling to keep himself upright for a day or so and died. Now there are 4 fish left. The long-finned zebra (my first fish) and long-finned leopard seem to be ok (though the leopard seems really fat) the other long-finned leopard is hovering around the same spot at the glofish was, and hasn't been eating today or swimming much at all. The short-finned danio will eat when hungry but hides under a pagoda hut in the evening (though I've seen him swimming around the tank in he morning before I go to work). So that's my story, I feel like I'm slowly killing my fish and I feel so bad! Here are some details about my tank: 15 gallon top fin that came with a filter and heater. I've not had the heater on as at room temperature it's already too warm at 78-79F. As I said, I used API stress zyme to prepare the tank and used it during my last water change again 1 week ago. I have well water which I treated with aqua safe during last water change. Last water change was last Saturday, about 10%. Water readings: 8.4PH and 300alkalinity (highest on chart so could be higher, thinking this might be the issue but have not found clear answer on how to consistently bring it down) 25 hardness, 0 nitrate, 0 nitrite and 0 ammonia. I have a few plastic plants, and ornaments and a dragon bubbler.