What kind of mechanical filtration does the bio-cube have now? BTW, what brand is it and how big is it? Do you have the room to add a layer of felt filter sock type material in with your other media?
I've been running a 17g tank I built myself with just a big HOB filtration system. But I added a lot to the stock filtration that Seachem offered. Besides their sponge media, I added 3 other sponge type filters and cut up some old filter socks and did 3 layers of that between the sponge layers. Now I have to clean it every week and I don't even have any fish in the tank. But I have zoas, lps and sps corals, a couple of Rock Flower Anemones and lots of CUC (Clean Up Crew). That includes lots of Astrea snails, Nerite snails, Cerith snails, a couple Emerald crabs, a couple of serpent stars, a couple of small sea cucumbers and a few others like limpets and clams (not the big pretty ones).
Carbon can help keep your water a bit more clear, but I don't find my water being very discolored. I even have a Tunze in-tank skimmer that I have used in my small, temporary holding tanks in the past. But I haven't been using it in this 17g tank.
I've been seriously considering getting out of the hobby after 20+ years. We travel a lot more now and the bigger tanks worry us some while we are gone and possibly putting the clean up burden on the friend who feeds our cat and the fish. When I sold my last 90g tank I thought I was done. But I had a few tiny frags and a pricey RFA that I put in a 5g holding tank. That's when I decided to give the smaller size tanks a try. The 17g tank has been running for months and even the sps corals seem to be doing well.
Now I'm just finishing the process of setting up a 40g breeder tank with a Fuji aio insert. It's probably a temporary tank. I've recently stripped down an old 40g rimless cube I built several years ago and re-assembled it. Now I'm working on what I want in a bigger aio insert for this tank so I can have better filtration (like a 4" filter sock) and can also fit the Tunze in-tank skimmer inside. I'd also want more flow from a bigger pump (the 40g breeder insert from Fuji came with a cheap little 500gph pump). I'd like at least a well made 800 to 1200gph pump with flow control so I'll have less need for wave makers in the visible part of the tank.
All this explanation is just to say, I don't intend to run any chemical filtration. I'll have a spot for it in the aio insert, but it won't get used unless some water parameter gets out of control.
