what should be in my sump
 

there are bio balls, magic mud, green algea and a heater

From what I know, avoid the bio balls ! - This is what I those expert advised me when I started and it make sense when come to the point that: have to do the cleanning for those balls weekly when algea developing.
But I'll tag along this post to see the "cool idea for this as I am having same concern as well. :lol:

Skimmer if your doing one, mud if your going to have a fuge in sump, algae in the fuge, return pump, heaters, reactors, live rock for extra filtration and baffels between your sections. Bio balls are nitrate factorys if you dont clean them regulairly and from my understanding they are for FOWLR through a trickle style sump.

I like Chaeto in the sump, but don't forget a light for it! You didn't mention it, but I think you must have one? :)

Ya, if it's a reef you should take the BioBalls out (slowly, like 1/4 of them each week) they are designed to catch detritus, and break it down into nitrates thus increasing biological filtration, which they do very well. The problem with this in a reef tank is the point of all the filtration in a reef it to prevent as much detritus from breaking down as possible (the point of a protein skimmer). Remove detritus before it turns into nitrates because only so much nitrates can be processed by the live rock and be off gased as nitrogen gas. If there is too much detritus breaking down, and the live rock can't process it all you will get nitrate readings when you test. In a reef you should have undetectable nitrates if you're doing everything right, but <10 ppm is considered "acceptable" by many people. Personally, I think any nitrate reading is unacceptable, but many people have difficulties achieving this. Usually due to poor maintenance or feeding practices or overstocking.

Ok, that out of the way...everything parkinsn said plus you could have a filter media in there or a filter sock. These are both designed to catch detritus like the BioBalls to keep your sump clean and remove the detritus, but the filter media is cheap to throw away, and the filter socks can be washed in the washing machine (no soap!) and reused. These medias should be replaced 1-2x weekly, but daily is best. I make a tray out of eggcrate in my sump where the water enters from the display and put a sheet of filter media on it. This makes it very easy to replace everyday when you pre-cut a whole bunch. Just change it out when you're feeding. Your hands barely even get wet, and it takes a whopping 15 seconds. :D

J&L carries bulk rolls of cheap filter media that you cut to size. My fav. http://www.jlaquatics.com/phpstore/s...t_ID=cl-fmedia