No amount of added filtration will help you with your nitrAtes. Adding a canister would only benefit if you were seeing ammonia or nitrIte.
I'm phasing out the use of all penguin/marineland HOB's for the alternative AquaClear HOBs and various canister filters though. The AquaClears have lots of room for biomedia, and if you cut the sponge in half lengthwise, I've found it doesn't get clogged as easily, and isn't as prone to harboring nitrate causing gunk.
Water changes, water changes water changes. Do you already have a water changer, or are you using the old fashioned bucket system?