I have a sumpless 55 also and I considered the Bubble Magus Nac 5e, Reef Octopus BH1000, Reef Octopus BH2000, Reef Octopus BH90, Aquamaxx HOB 1,Super Reef Octopus LX1000, and Super Reef Octopus XP-1000S HOB. I ended up buying the BH90 but it isnt here yet. I would imagine the BH1000 and BH90 would be enough for a moderately stocked tank. If you have a heavily stocked tank, then the BH2000 or the super reef octos would be ideal.