Hi ,ive rescued him 2 weeks ago and he is currently in quarantine of 60L with filter and oxigen. parameters are 0,0,10. During all this time he was happy and active but during the last 2 das he seems lethargic , spending alot of time on the bottom or just floating in the middle of the tank. He is eating and hes poop seems healthy, and i dont see any external signs of something wrong What do you think?
The situation could be due to a range of factors, including potentially the stress of the move or a change in water parameters (e.g. PH, hardness). Presumably the filter media is cycled i.e. it was in use in another tank occupied by fish, or the beneficial bacteria kept 'alive' by adding ammonia to mimic fish waste, up until his arrival? If not, then it could be / could have been going through a mini-cycle even although your current water quality seems fine.
Keep monitoring water quality at least daily and do several water changes of up to 50% each throughout the week, which should help ensure any other aspects not measurable by home-based test kits (e.g. stress hormones) are kept to a minimum and to ensure that ammonia/nitrite/nitrates remain at the level you have them.