Welcome to the forum....
To understand....he has a behavior change right after a 50% water change....correct.....if so....make another 50% water change using like temp dechlorinated water and dose the dechlorinator for the full volume of the tank....
Often when you have a sudden behavior change after a water change it is due to-forgotten or not enough dechlorinator, extreme water temp or pH changes, contamination of some type........
Filter media-needs a rinse/swish in old tank water a couple of times a month with one of the twice weekly water changes and if you plan to use carbon (not needed) change this per package direction....
Good luck and keep us posted....
To understand....he has a behavior change right after a 50% water change....correct.....if so....make another 50% water change using like temp dechlorinated water and dose the dechlorinator for the full volume of the tank....
Often when you have a sudden behavior change after a water change it is due to-forgotten or not enough dechlorinator, extreme water temp or pH changes, contamination of some type........
Filter media-needs a rinse/swish in old tank water a couple of times a month with one of the twice weekly water changes and if you plan to use carbon (not needed) change this per package direction....
Good luck and keep us posted....
