Turn Fluval into a tricle filter?? That's new, How'd you do it? Not that I will do the same, just curious. All biological filter will produce nitrate. However, if you clean your canister often enough before the detritus has a chance to oxidize, you could've avoided nitrate. Now, that's pretty hard to accomplish, especially in a mature tank.
Using LR in the sump act as biological filter/bioballs. Just not as efficient as bioballs. Why not pull the LR into the main tank, Add a canister as buffer against ammonia and nitrite spike, and another protein skimmer? LS optional.
If want DSB, why not put the DSB in the sump and grow macro algae in it with a pod farm. DSB does not work that well in FO main tank as there are too many digging fishes for FO that will disrupt the balance of DSB.
[ August 16, 2001: Message edited by: danmhippo ]