I’m sorry but you’re not very clear in your description. Are you saying your fish is swimming down into an upwelling of current caused by the filter flow? Is the clown breathing normally? Are the rest of the animals in the tank ok? What is your tank setup (size, filter type, skimmer, live rock)? How do you make your seawater how often and how much do you change it? Most of the clowns that I have owned over the years lived in a corner of the tank bobbing up and down for a month or two before they settled into their host Anemone. Without a host your clown may never feel at home. In one Clown tank I had there was a floating glass thermometer that they bobbed up and down by wherever it moved until they moved onto their host about four months later. All I’m saying is that many types of clownfish swim in a bobbing motion in one spot. If you can try moving the filter outflow and see if the clown follows the current (note this may effect other thing in your tank be ready to put it back in it’s original position if need be). It may just like to swim in the upwelling is all.
If you’re saying that you had other clownfish that died (got sick) and this guy’s acting the same then you’d know better than me what the future holds. If you do lose your fish I’d encourage you learn all you can before you try again and be prepaired to spend $$$. Learning on the fly can make for a lot of expense and heartache.
Good Luck
