Hey everyone, I have had my 10 gal tank with 6 cherry barbs and 2 amano shrimp for about sixth months now. Everything has been going rather smoothly up until now. I know the tank is slightly overstocked, but Nitrite and Ammonia levels have remained a consistent 0 throughout the whole time, and there have been no problems fighting whatsoever. Yesterday I did a major change on the fish tank, replacing gravel with Fluorite Black, new wood, and new rocks. All other fish and shrimp seem fine, and after testing Nitrite and Ammonia, still a hard 0. However, one cherry barb is laying on the sand, un moving, but alive. He will occasionally move to another part of the tank, but other than that, no movement. I see no signs of disease, fights, or anything else. Please help!