i have an approximately 4 year old elongatus who recently has lost interest in food, had rapid gill movement and has been trying to hide in the back corner of his tank. Ive had him without issues since he was very small and have had experience with other piranha as well so i can generally snuff out a problem early, but this has me flummoxed! it's a 100gal tank with a powerhead, 2 75 gal filters, and substantial aeration. i know all signs point to water quality issues but all the water parameters in my api master kit are fine (ph 6.8, ammonia 0, nitrite 0, nitrate 0-5). temp is a constant 77. he is housed by himself and is fed nothing but dead, no live fish or other animals apart from small snails in the tank with him. the only chems i use are prime water conditioner and seachem substrate tabs for the plants. the only thing i can think is i moved about a month and a half ago and had to take down the tank then put it back together but ive done this before without issue and made sure to save as many as the beneficial bacteria in substrate and filters as i could. plus like i said the water perams look fine. is there something else im missing with a different water supply that may be causing this? could it be some sort of disease? im stumped! I guess I should also say that up until a few days ago he was his completely normal self. Eating, chasing people by the tank etc. Any suggestions?