You have to try to get him to come to the surface.. If he eats thats usually the best way.. then just flick the net right over him..
My blenny just died today.. he was even eating a bit too.. but this is the time you might still be able to save that clown, later on he'll be all out of energy and just die.
You gotta get him out of there, and maybe he will get better if he's by himself in a tank. My clownfish was similar to what you describe when I bought him, he slowly got better and his appetite grew and now he's happier than ever before.
You also have to consider it's stressful to move him, especially now that he has barely any energy left.. he could give out his last ounce of energy running away from the net..
Another thing you could try to do is remove the LR
you added, maybe that had something to do with it.. and do a lot of water changes. This is a lot of work.. I understand you care about the fish.. when I went to the LFS
they told me its cheaper and easier to just let my blenny die.. I still tried to get him better but it was too late. You might still have a few days.. I read somewhere than he could go 7 days without food.. maybe longer.
Also, what are you feeding him? I just noticed that I was feeding my blenny "expired" algae.. I thought it was brown algae, but it was actually green that was so old it had turned color. I can't believe the LFS
sold me that stuff like that.. I don't really know if that had anything to do with the fish dieing, but I dont think extremely old algae was good for him..