Clown fish seems hurt? or sick?
 

Thanks for reading. I just added a sump to my system, 5 years old established reef tank. And once I got it running one of my clownfish was riding the current around the tank like crazy all day. He seemed to love it. Now a few days later, hes acting/swimming really weird. I find him mostly sucked up to the overflow where hes barely moving. Then when he sees me he swims sporatically, sometimes sideways, upside down, and seems to have like a "crook" or cramp to one side (his body is not straight).

Anyone have any idea what might have happened? What I can do for him?

All other tank mates are perfectly fine, coral all perfectly fine, everything seems good except him.

Clownfish can be pretty strange sometimes.

Was the fish quarantined?

When you say swims upside down, do you mean nose down or literally upside down? If the latter, then something's not right. Possible injury or has air in his swim bladder? I'd keep an eye on him and keep him well fed(assuming he is still eating)

Any visible signs of disease?(rapid breathing, head twitching, "dusty" appearance to the skin etc.)
If the answer is no, then he will probably be fine and is being a clown.....

As for hanging out by the overflow, he's probably hosting it and then gets excited when he sees you thinking he's going to get fed.

Hope you figure it out. Good luck

Yes I would also suspect swim bladder. Unfortunately I don't have a treatment for ya.