Here is a photo of my second denitrator. As written earlier, I use 6mm airline hose wrapped around a 4 inch PVC pipe. The water comes from the overhead refugium and is gravity fed down the airline coil and is robbed of oxygen by bacteria that has grown in it.
It reaches the bottom, goes through some rubble, then some LSM (Carib Sea granulated sulfur), some ARM (Carib Sea Aragonite Reactor Media), RowaPhos, and finally 100 grams of GAC (Granular Activated Carbon) at which point it hits the overflow and goes back down a 1/2 inch pipe to the sump.
By doing the above, I have managed to keep nitrates and phosphates to zero and keep calcium at 450 and pH at 8.2
. The only drawback is the unsightly pipe next to the tank, but it is a work in progress
. I will be releasing the undulated trigger, clownfish, puffers and the lot back to the sea on my next trip and probably go back to a coral/seahorse tank though I need to build up a sizable pod population first.