I do large and frequent water changes...close to 100% per week...when I am home. However, for the past 10 years or so, I have frequently been absent for three weeks at a time, and home only for one week between those work rotations. At first, I was pretty worried about my water quality when I was gone. My wife, like the vast majority of non-aquarists in the world today, proved to be completely incapable of merely feeding fish; she always overfed to the max. I quickly switched over to miserly pre-measured portions of food and a written schedule for dispensing it, and that problem went away.
I would do a roughly 90% change the day before I few out to work, then another 90% change when I returned. Essentially, I had a 180% change one week, and then nothing for three. I am also a proponent of easily-cleaned filters, because I like to clean my first-stage mechanical filtration daily when at home. This daily cleaning was not done for the three weeks I was absent.
In my tanks...not at all crowded with fish, heavily planted and sparsely fed...nitrates would typically climb to 20ppm or so by the end of three weeks. That first 90% change when I got home would drop this to undetectable levels (my well water has zero nitrates) and "home week" which incorporated fairly generously feeding by me, the level might start to become noticeable by the end of that week, at which point another 90% change took place. 20ppm is not ideal, but of course it wasn't that high for the whole three week absence; it just rose to that level by the end of that time period.
Do a big change just before you leave; do another one when you return. You state that you only do a change every two weeks now, so if you are gone for a month you are really only missing one change; not ideal, but you should be fine.
Now...let's chat about why you only change water once every two weeks normally...
