I have 4 green neons, 2 black tetras. 25 gallon tank. I have and air stone! So I doubt it's a problem with oxygen. I got the black tetras 4 days ago, they were very active, eating, and all. I added the 4 green neons 2 days ago and they were very active as well My tank is 4 months old, been running the whole time, I tried adding fish (6 fancy guppies) 2 months ago but they stayed at the top of the tank and after a few days died. I let my water cycle for 2 months, after doing several water changes. I've tested my water, and all the perameters check out, I'm worried about my fish, they keep opening there mouth maybe 2-3 times a second, they stoped eating as well. They stay at the back of the tank at the bottom. But they still move around alittle, what could I try?