Just to summarize my experience with my biocube.
I did try different lights to experiment with the corals, first lights were the stock Power Compacts, while the spectrum color we can see is somehow nice, I believe it helped very little in coral growth, the tank had mostly zoas and a couple LPS, the lights lasted less than 5 months and then it was removed.
Second light was a 75 watt metal halide and a couple strips of panorama LEDs, gutted the lid and leave the stock fans on it to help remove heat, tought this light was going to be much, it didn't, after some time I notice recession in some zoas but others were doing just fine, I can't complaint all solely to the light and other factors were playing.
After this MH I had tested T5's plus the panoramas, got the hood removed and placed an acrylic cover and put the fixtures on top of the trim, this had the tank looking brighter than any other light, I had 3 x 18 watt actinic and 1 x 10k, this combo of LEDs and T5 was really nice and the last I had tried un the biocube, I can say the tank looked fine and gave the corals a nice pop.
Other things I've tried in this biocube were the skimmer, algae scrubber, HOB filter for chaeto and the rest of the equipment.
I didn't have much luck trying to grow chaeto in the HOB filter or in the middle chamber, I might had never found the right spectrum light for it, chaeto would receded and clumped, light used were a bulb par 38, not even the needed for chaeto too. Gave up with it.
The first skimmer I tried was the Fluval sea mini, I think is a good skimmer but not for this size tank, couldn't do any skimate after around two months of using it, skimmer is rated for under 20 gallons so that's a good reason.
Second skimmer was the Eshopps nano, this one performed excellent, can't compared with bigger skimmers but this is the best in their range, lots of skimate, not so dark, more light and wet but consistent, could find it sometimes with the foam expelled out of the lid.
After the skimmer I decided to give a try to an algae scrubber on the middle chamber, after around 3 weeks the screen on the scrubber finally matured and was able to remove algae, the light was a Flood light LED, it did great, I could remove substantial amounts of algae week after week after using this combo. The only downgrade I had to remove the skimmer, noticed that some algae started to grow in my rocks. After noticing this I just added the stock skimmer, I did modified, smaller limewood mini air stone, bigger chamber and bigger air pump, it did some foam but never a great cup of skimate. The algae on rocks were controlled with water changes.
Summary.
After all this I finally were exhausted, while the biocube looks good I really love to have bigger tanks and put all effort on them. I can say mine required constant maintenance and mine wasn't even overstocked with corals or fish, I've seen beautiful, flourishing biocubes. Not saying all biocubes require the same approach but mine did. Loved the journey and actually now I'm setting another nano, this time a 10 gallons halfmoon tank.
Thanks for reading this long post.