DIY De-nitrator Questions

[JordanM]

I am looking at making a de-nitrator that will be relevant for both fresh and salt water. It will be for a 54 gallon tank. From what i have read you should coil 50ft of 1/4" tubing on the inside of the reactor so the water coming into the bottom of the reactor is anaerobic. I am using water filters like the one in the picture below and 50ft of 1/4" tubing will not fit inside of it so,
1. Is there a reason that the 1/4" tubing needs to be inside the reactor? (to maintain temperature for the bacteria?), or can the coil be located outside of the reactor?
2. How long of coil should i use? It seems like the consensus is 50 ft, but can you ever de-oxygenate the water to much by having to long of coil?

My plan is to make one like below that will have three filters. The first will just contain a filter to filter any debris out of the water that can easily be cleaned and dumped out if it gets plugged. In between the first and second container i was going to put the 50ft 1/4" coil and then enter the bottom of the second container that will be filled with Bioballs and the third container i was thinking about putting in the Seachem De-Nitrate Filter Media. Of course any of these containers could be switched to sulfur at anytime. I would like to use this for freshwater right now but i will be changing this tank to saltwater eventually.

Please let me know your thoughts.