worried about my syno catfish

[skelf23]

I have a 64l tank with 5 neon tetra and just yesterday introduced my new male and female catfish.They were both quite shy yesterday but tonight the female is much more active and seems to be enjoying the new found attention but i`m concerned about my male.Although he has been exploring his new home i have noticed that when he comes to rest at the bottom of the tank he just seems to take a nose dive straight to the bottom and ends up lying on his side or back untill he eventually flips himself over.Is this normal behaviour as my female tends to turn before she reaches the bottom and comes to rest on her stomach.Any help or advice would be greatly appreciated.

Many thanks

[VoidParadigm]

Maybe he has something wrong with his swim bladder and therefore can't swim properly to the bottom?
Do you have a test kit? If so what are your water parameters?
It is possible that it's just an example of weak livestock.
Do you know the species of syno, or do you have a picture?