OK, I thought the second link worked, but it clearly doesn't. The articles of course refer to reefs rather than planted tanks, which are very dissimilar in some ways but I thought you might get the feeling there was a general point here.
People tend to assume, and this is a vey common trait, that the only measure of pollutants are those measured by the classic nitrogen cycle. But this is not the case. The first step of the nitrogen cycle for many waste is not the metabolisation of ammonia to nitrite , but the destruction of organic waste to ionic ammonia/ammonium and for some organics, and it's more than a trivial percentage, this is not the case. Thus these things accumulate, along with phosphates, metal ions and others.
Now your plant growth will consume and bind many of these things, but not all, and I don't believe it's all predictable. You are feeding your tank, are you convinced/certain that everything you put in is utilised or removed in some way, and that all wastes are removed, not just the ones you measure.
You could measure DOC electronically, or get a redox meter. You're right , your high kH is useful in keeping pH relatively stable as it will overpower the acidification effect of accumulating organics
As a final note I find it interesting that you're keeping fish from an enviroment of continual water changes (high oxygen stream/rapid flow river) to one of no water changes. When I was interested in L number plecs which are somewhat similar I became very familiar with water changes |