If there is flow on his foot, He will most likely keep moving. This requires a lot of energy from an animal that rarely moves in the wild. This may cause it to continually weaken over time, leading to it's death. This is IF a power head or some other animal in the tank doesn't kill it first. While there are very few absolutes in this hobby, I think keeping a Haddoni in a BB is a bad idea. These animals should have a sand bed, with a rock it can bury it's foot under. A high flow BB SPS tank is not the environment for a Haddoni. I hope you change your mind about this addition. It could cause the death of not only the Haddoni, but some of your SPS as well. Good luck with your decision.