I am thinking about modifying my sump a bit. Currently I have a 55 gallon display with a 15 gallon sump. Because the sump is so small, I want to make sure I'm making the most out of what I have.

Replacing the sump with a bigger one isn't really an option now due to the size/shape of the stand. So, the main thing I want to do is remove the bio-balls from the first chamber. Would it be possible/good idea to replace the bio-balls with arag-sand? I could probably have a sand depth of around 5 inches in the first chamber. Would it be better to use live rock rubble?

I also believe that the 3 inch sand depth in chamber B is probably not ideal so I may have to deal with that as well. I'll also look into adding some macro aglae to chamber C down the road.

I've attached a quick diagram of the current sump set-up and welcome any other suggestions.

Thanks!

http://api.photoshop.com/home_473cfb67dd7c40b7ac00ff5adda40275/adobe-px-assets/adc6de3c691c48e8bc900b2e3464a263

I think that pulling the bio-balls would be fine. If you have been using them for a while I would remove 20 - 25% at a time so your biological filtration will catch up. A 3" sandbed is not quite deep enough to establish an effective anerobic zone. I would increase the depth to >4". I might go with LR in the A chamber because I think the inflow would crater the sand, possibly even deep enough to affect the anerobic zone. I would not use small LR rubble but bigger chunks so they trap a minimum of detritus. The rock will need to be completely submerged or it will just work like bio-balls.