Hello everyone, I am a newbie to this board and to the fish world. I started an aquarium about 4 months ago. It is 10 gallons. All of the fish that I have purchased have perished, I presently have a redtail shark that seems to be the most hardy as he is still alive(I have had him for about 3 months). I recently purchased 3 balas and just today one of them died. I don't know all of the correct terminology when it comes to the tank so please bear with me in my explanation. I have a filter that has the sponge and carbon (I think that this may be the Interal box filter?). I also have another thingy that is green and bubbles come out! (Excuse my lack of knowledge here) I am also testing for N03 and N02's the N02s are perfect (clear). The N03 are around 10-20. Last night the Bala seems to be vertical alot and I thought that there must be something wrong with him but my lack of experience left things at that. When I saw him dead today and another of my bala's doing the 'vertical' as well got me scared. All three of them are babies, no bigger than a small goldfish, so I am hoping that it is not the tank size. I try to change the water whenever the N03s go over 10, maybe ever week and a half. I love my bala's does anyone have any suggestions for me to save the last two?