I just briefly browsed through this thread. I'll put my .02 in on it. First off, I think the research that was done on metals was somewhat controversial, seems like Pro or Farley one has an article with some of their concerns about it. But it has been a while since I ran across that and don't recall exactly. Definitely there were some salt mixes that were of concern. Maybe it was that the article was just old and salt mixes have advanced.
Like I say I cant recall exactly. Somebody pick that ball up and run with it? Also according to Randy Holmes Farley, the sizes and frequency of doing water changes isn't whats important so much as doing them. Based on doing 30% monthly. In other words, if you have 100 gallons of column, it doesn't matter that much if you do 30 gallons at once, 15 gallons twice a month, or 1 gallon a day. But just doing them. Now, with that said. I haven't done a water change on my 135 since July. when I did a series of changes that amounted to 100 gallons. I am very much do one now. Also I'll add that just changing the water is good, but you should try to remove as much crap as is safely possible.Dusting and stirring up the detritus on the rocks is generally a safe thing to do and should be done IMO at each change.
Now, on the nitrate issue. Any properly set up system that is properly stocked/fed will not have nitrate issues. If you have enough LR and an adequate, well cared for NNR sand bed, your nitrates should always remain low if not 0. Stirring the SB gently is necessary for proper function. It should have ever be done very carefully. Gently stirring the top portion of it only in small sections at a time. Being careful not to stir it up, but just stir it around...Make sense? If you are doing water changes to remove nitrates, then of course you are limiting the size of anaerobic bacteria in your system. However if you LR and other NNR mechanisms are not adequate this is a necessary evil. Each system is unique in it's own individual needs. This should be taken in account. Just as it takes up to 6 weeks for aerobic bacteria to grow large enough to handle the DT's needs, it will take anaerobic bacteria some time to grow also. Possibly 3-4 weeks. Again this depends. Additionally, it can become depleted if there is no food (nitrates) for it to process. because you are removing them via WC's.
Now, I'm not advocating not doing water changes at all. Definitely they are beneficial to our