Hard to say for sure without seeing them, but likely they're fine and that's normal. Clowns live up to their name. They're "weird" compared to what most people think of as normal fishy behavior like a tang or wrasse that constantly is swimming or gliding around the tank seemingly effortlessly. Clowns always look like some kid at summer camp that can barely swim being shoved into the lake to "learn". However they're just fine, they just look a bit awkward. There are many people that keep them in a high flow SPS tanks and the clowns keep up just fine. I can tell you from years of diving that the currents and flow at many real reefs far outstrips what you likely have in your tank and these buggers do just fine. Just keep in mind that you can't judge their health based on comparing their behavior to open water swimmings like tangs or wrasses because clowns are not at all the same. They tend to like enclosed secure places (like anemones) and will generally just flutter around that area most of the day. Especially if they're new they're going to explore and move around, but not like many other fish. They'll hang out in one area, then another, then another. Eventually they'll find a spot that is most comfortable and "host" it and spend most of their waking hours around that. If you're lucky, that place will be a cool rock structure where you can see them. If you're unlucky that will be a power head or overflow box lol. The warning signs you want to look for are very rapid breathing, especially if the clown is coming to the surface and looks like it's sucking air. Just being near the surface isn't cause for concern, because again, clowns are weird and will do stuff like that. However, if you're testing for ammonia and that's 0 or very, very close to it, you shouldn't see that behavior at all.