The Oceanic filtration system is much better thought out. My brother just got a Oceanic and I loved the way it operated. The hood was nice and secure, The filtration comparment has it's own door to access it, there is a water level indicator on the outside of the tank to let you know when to add more water, and the wet/dry system they have going was really well thought out. There is plenty of room to add stuff to avoid cluttering your tank (heaters, skimmers, stuff like that).
JBJ just seems cramped. The filtration is really just a series of baffles behind the tank to move water with sponges (Bioballs per instructions were removed as they say only to use them for FO tanks...but I have issues with bioballs reguardless, as do many reef keepers). I have 7 tanks right now from 5g to 125g, and the Nano Cube seemed to be the worst. I do everything the same to all my tanks, yet the JBJ always seemed to have a cyno outbreak every couple weeks. The only way to avoid this was constant water changes every 4-5 days. I had 1 cyno outbreak in my 29g tank awhile ago, but ever since then, nothing. I guess it could have been my fault, but the only things in there were a watchman goby, a maroon clown about 3" long, and a lawnmower blenny. I had some CuC in there as well, 3 peppermint shrimp, 10 Tiger Trochous, and a few hermits. The sponges almost have to be taken out every few days to clean them up because they get clogged pretty easily (which probably had something to do with the cyno). I didn't like the tops, the little sliding arms broke on me, they are really flimsy and cheap. The lights are a pain to replace, there are like a dozen screws to remove the cover to get at the fixture. Just in general I think a shoddy product. I never over fed that tank,any more than I overfeed my other tanks (which I don't). I don't have any cyno problems in any other tank, and most of them don't run skimmers, so it's hard for me to figure out why it was such a problem in that tank.
It just seems like they threw out a cheap product to get in on the Nano market. I had 30-40lbs of LR in there, and a nano skimmer, and it still didn't really help.
If you look at the design features of both tanks side by side, you'll probably see why I like the Oceanic better. It was thought out much better IMHO.
I guess if I got one cheap I wouldn't complain, but I paid like $250 for mine plus stand. I could have gotten a larger Marineland system with a stand for that price. I have a 37g right now only using the stock filtration and 20lbs of LR with more fish than the Nano ever had and have yet to have a problem in that tank (no CuC because of the fish in there).
The only thing the nano is being used for now is a QT tank. It just gave me to much of a headache. Maybe if I drilled the back out and made a sump for it....hehe
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This is just my experience with it. Some people probably have them and love them. It just seemed to be much higher maintenance than any of my other "cheapy" tanks, which I disliked the most.