A dwarf lion is not good even in a 40. They get about 5-6" ....."dwarf" is just smaller than the volitan. Also, if you are keeping coral, I would not use those scrubbers at all. I would probably use live rock as my filter, along with a skimmer and maybe a filter sock. You could still use the cheap tub if you like, but you are going to need an auto top off to keep the water level constant, or instead of cutting the bottom of the bucket off, use the bucket whole, and let it overflow into the tub. You can put your skimmer inside the bucket and the water level will remain constant.