You can certainly run a tank to some degree without doing water changes, lots of hobbyists have done it in different sized systems. The problem is the limitation that puts on your system. When you do water changes you're doing more than just removing nutrients. You're adding a lot of trace elements, trace being the key term here. Meaning they're immeasurable by today's standards unless you work in the right lab. Does that mean you can't grow certain corals, or have certain inverts? Probably not, it just won't be an ideal scenario, since you can't dose what you can't affordably measure.
OK, I am going to agree and slightly disagree with you here. I think you are correct, but not just because of water changes. I think there is no currently known method we have that can fully duplicate natural conditions to the point that we can keep and breed any species that are thriving, with or without water changes. So I guess it would be up for interpretation how you would set your "goal" or how you would measure success
while doing so with no water changes. And I think at a certain level it would become difficult to say how your method and setup is limiting you. I guess if you are arguably just as successful compared to most other hobbyists systems and methods, but doing so without water changes, then you are there. If you only manage to keep blue damsels, well so what, right? This is either fair point or a pointless and unprovable argument, or a combination of both.
We are not at the point where we can exactly mirror the natural environment, even if you piped in real "perfect" seawater, the aquarium environment would still present differences that would hold you back, size if nothing else. One of the things I would point to on this is our ability to breed different species.... it's getting better, but still only a subset of what we would like, and some of that is only achieved with hormones.
If your point about the trace elements is that it is just impractical on the "hobbyist" level, then yes. Most of us are using artificial sea water mixes, and likely those mixes are made by people with the "right lab".... likely a $100K+ gas spectrometer among other things. Almost the whole periodic table is in seawater, including plutonium and uranium in very tiny amounts (I took 3 years of chemistry). That being said, I think that not all of those elements are "biologically useful"...
Some other points on this:
- The DSR guy is making his own salt mix, and as far as I know he does not have the "right lab"... but for sure he is at an extremely advanced level with the number of tests he is doing and the elements he is tracking and dosing. I am still struggling to wrap my brain around it. If what he says he can do is true, he is growing most corals like weeds and only having difficulty with a few.
- The Triton method, sending your sample to a lab (would that count as the right lab?) tests for far more elements, probably getting close to all of them, perhaps already more that the biologically useful ones.
- And still, I think even if you were able to test and dose for every known element or compound, that still would not do it. From there I think ever more obscure issues would arise, likely complex organic chemistry issues that would take full-out scientists to deal with, and even then would only take you so far at our current level of understanding.
So, I guess in the end my personal opinion is that water changes are a somewhat "crude" method that I think would be interesting to get away from, and a worthy personal achievement in the hobbby. Now, it may take $20k in equipment and chemicals, take more time that it would have if you were just doing the water changes, and possibly at a lower level of "success", that is all fair. And for these reasons some may point at me and laugh because their $500 DIY + water changes gets the same or better results, that's all fair game I would say.
I am learning so much even researching these things, it is great. I have always wanted to do these things but never had the money, and some of the things I needed or wanted were never available until now either. At some point I would also like to go back with what I learn about reefing, and apply it to some freshwater setups I used to do, I think I could do some amazing things.