I found a diy project using de-nitrate in a plastic water bottle with a tube going in the bottom and one going out the top. You put a little foam on the top and bottom of the de-nitrate on the inside to stop it from entering the tubes. You then pump water with a power head or small pump through the tubes and de-nitrate.
I made one and it worked pretty good. It gave me a little trouble due to the space I had so I went out to buy something a little better to put the de-nitrate in. I ended up almost getting convinced to buy a canister filter and not use the de-nitrate at my lfs
. But I didn't give in, things are over $300 anyway. But I found a used canister with empty trays. $40 bucks, I snagged it and was able to fill one and a half of the trays with the de-nitrate I had. The pump built into the canister was shot, so I just ran a line to the pump I bought for the diy project, thing works great.
My question is, I still have one tray. I was wondering what I should put in it if anything. I could also take out the de-nitrate in the one filled half way and have two open trays. The trays are about 4-in diameter and about 2-in deep. Any advice would help.