Maybe. Had it turned down to a trickle I think but really can't remember. Anything can work as a denitrator if the flow is slow enough to allow anoxic conditions to occur. Goal is to try and keep it from going completely anaerobic but don't think that would be an issue with a little flow. Depending on the size of the canister 50 gah may be way too much.
I had good success with a deep sand bed as well that I had on my first tank back in the early 2000s. Thinking of doing this again w/ the 125 that I still have and tying it into my retirement build--which will be bare bottom. Stick a plenum in there and maybe plant mangroves.
Good luck. High nitrates can be easily fixed, you just need to find what works for your system and have the patience to give it time to work. If no improvement after 8 weeks or so, re-examine your situation.
