Hey guys a few months ago i got 3 corydoras and they were doing well and swimming around, but recently one out of the 3 has been staying in the back corner of the tank all alone and wonāt move. he definitely is alive because i kinda nudged him out of the corner with a net because i was worried myself he was dead lol but he wasnāt. but after that he was out for a few minutes and then went straight back to the corner. the other two are happy and seem like they are growing well they play with each other all day. yet this guy looks like heās getting smaller. iām assuming itās because heās staying in the corner heās not eating. my water quality is all good Ph is at 7.0 and i do a 50% water change weekly. iām just worried he is sick? iām not sure whatās going on he usually plays with the others until recently.