First you have fish and you feed them a lot so this will happen. Since you also have fish and no corals having nitrates at 60ppm isn't a problem. My tanks are loaded with fish, with no live rock, and I don't even bother to check for nitrates. I just make sure that my Ph and SG are stable and I watch my fish and make sure that they look healty and are eating well.
Since you Don't have a reef tank don't apply the same standards of having to have nitrates close to zero.You have a FO/Fowlr tank and with having a lot of fish your going to have nitrates but this isn't a problem.
If you want to bring the nitrates down you may need to add more live rock, do a larger water change or feed less. Also look for things in the tank or sump where debrie and junk maybe collecting and try cleaning it out. Also what do you have on the bottom of the tank sand, crushed coral or bare bottom. Crushed coral if not cleaned regularly will cause high nitrates and will sand.
Not sure why your running a Diation filter, I would think that it's only every so often to polish the water.