I used that link to describe DOC's. I also run a drip that changes 30% volume daily, so I agree the water changes will be the most effective way to reduce the waste in a system, but sweeping 20% under the rug it still what it is. Run a skimmer on a reef system and you'll "see" what you often don't. But if you don't "clean" your filters for a year, then how could you possibly know that it's clean or not? 20ppm shows that there is something still in there. If 20ppm is good for you, then so be it. I prefer to shoot for as close to zero as possible ....
and I keep a large female jag solo in a 90 and feel I'm at my stocking limit. Opinions will vary. I really mean no offense when I posted the original post but new keepers often get into trouble by thinking they can go months, or often years without doing maintenance and be fine, usually based on threads like this. I can go 3 months without doing water changes and never hitting 20ppm N03 on one of our systems, but would advise against it for a number of reasons.
Bottom line? clean your filters regularly and you'll have healthy fish. Im sure your jag is fine at 20ppm, but a new keeper may get the wrong message.