Its is a standards 12 gallon nano its the one with the built in wet/dry in back. I use Instant Ocean. My LFS only carries that and Coralife. But the Coralife is only in a Large bucket that cost nearly $50 so I just buy the bags as they are more afordable at the time I need them. I think it may have to do with the critters in there. there are 3 fish 2 of which will move to a better place soon. snails, hermits, a very scary worm that i just seen tonight. and little itty bitty bug things. It could also be the o2 thing though the clown in there has been acting funny the past couple of days like skimming the top of the water and such. I am schedualed to do a water change saturday but I may have to push it forward.