Well, all I can say is if I had to change 90 percent of the water twice a month, I would have given up the hobby soon after I started. The problem I see here is you are assuming my friend, that you will somehow get improved water by removing your skimmer. Your skimmer certainly isn't adding to your nitrate problem. At any rate, if you are willing to change that much water on multiple tanks every 2 weeks OF COURSE you will have better water, assuming you are not adding phosphates, metals etc., with your water supply from the tap. To me, it sounds like way too much work for what is supposed to be a relaxing hobby... some would even suggest it could be unhealthy for the fish, especially if you start slipping and are not keeping up with the rigorous schedule and changing that much water less often. Massive water changes on older, established tanks can create PH shock, which is far more stressful than the nitrate issue you're worrying about.