Diy sump for biocube 16

[Diveks]

So, this biocube is an sps tank, it has been running for about a year or more, a few months ago i had to go out of town and other people were caring for my tanks, sadly nobody knew how to dose and stuff so my sps tank crashed, although one large colony actually survived the crash. The tank is well now and everything is thriving, though i have an algae problem since the first time i ran the tank. I have a tank lieing around that i want to use as a sump, it is actually bigger than the biocube. Ive seen people doing this but im not sure what i should put in the sump. Should i just make it a fuge or should i use a skimmer or reactors? Im not sure what small skimmer ks actually useful since ive had a hangon the back that does nothing. I can also find a bigger one if it can be useful for the reef. If you can, can you give me the skimmer or reactor i should go for? (if you think it is better than a full on fuge.)