Hello, at the office i work at i inherited a betta fish in a tiny little bowl. There was also a jar in the cubicle next door to me with two mollies. I started looking up how to take care of these fish and realized that neither fish could be happy in such sad conditions, and so i got a four gallon round tank which i set up at my desk here. It was the largest tank i think i can get away with without bothering anyone at work. I put the mollies and betta together, and the mollies seemed much happier but my betta got even worse. (though he was never aggressive toward the mollies.) He passed away yesterday. It was very depressing. I was going to get another betta but i think i might just stick with the fish i still have. Also, I have three small glow danios and an albino pygmy placo that i bought when i got the new tank. I know that my tank is a little small, but it has an air bubbler and an under gravel filter on the bottom. I change about 1/8 of the water every few days, and i treat the water before putting it in the tank. The betta was in the tank with the other fish and when i came in yesterday I saw he was at the bottom, and was..dead. I had really grown to like him and it was upsetting. I was wondering though, why didn't he float to the top of the tank? does that mean anything? And also, he had a very grey color to him. I did an 80% water change and cleaned out the whole tank with warm water just to be safe. Today all the fish are doing good, but I am new to this, and would appreciate any advice anyone might have about my situation.