I think trace elements are one of the more interesting elements of all this, particularly because we all know you can be successful without spending a lot of time worrying about them. There are simply too many tanks based on basic 2 part or kalkwasser to argue against that fact. Supportive of that, for the same reason that water changes don't maintain calcium and alkalinity levels in these tanks, water changes are also not a realistic solution to maintaining minor or trace element levels. So levels are likely significantly depleted in a majorty of these tanks, and it is not preventing their sucess.
For a majority of my personal reefing adventure, I have felt most of us shouldn't dose anything that is unnecessary and expensive, doesn't produce definable and easy to identify results, or anything you can't test for. I think that thought process was largely founded upon not only making this affordable, but also easy enough that the average person can do it. I still think this is sound advice to a vast majority of reefers.
The element that has changed in the last 5 years for me is an understanding that everyone's goal is not the same. Some of us just want a reef tank in our homes, but many reefers want a hobby and want to continually hone a skill and their knowledge on the subject - All of which span a wide breadth of available space, time, budgets, and other resources. Honing skill and knowledge can be expensive but almost always has more failures than sucesses and certainly very time consuming...
So in that spirit, I think the real question isn't "can you be successful without dosing trace elements" because I think the answer to that question has already been answered and is not really debatable. The question is "are there real benefits to maintaining trace elements that justify the efforts and results?" I guess at this point it is hard to believe that maintaining natural sea water parameters won't have some benefit - but are the results worth the time and effort? This is really an individual goal question that likely doesn't have a universal answer.
Someone brought up the vitamin c analogy which is at minimum an interesting thought process worth exploring. Almost 99% of the human body is made up of just oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. The last ~1% is minor and trace elements, minerals, and vitamins - many of which are almost universally agreed to play major roles in your overall health.
Somewhat similar to what we are discussing today, I think you could survive for decades on diet made up largely of water and Big Macs. However, a complete diet rich in minerals and vitamins will almost certainly increase metabolic health and growth, provide denser bone structure, sharper vision, and immune response - all the types of things that go with providing your body the elements required to regulate and promote healthy biological function.
Now, corals are pretty far from the human body so this is not a fair comparison, but even looking at less complex lifeforms like wheat, the reduced availability of a single trace element like Molybdenum can
reduce the ability of the plant to utilize nitrogen and related growth by
30% before symptoms even become apparent. There is a lot more to all this than most of us reefers will ever fully understand.
Still, this doesn't relate to corals directly. Sadly, there just isn't a lot of legit research done on the role of trace elements and a variety of coral species, and there probably won't be a lot of this type of research in the foreseeable future. So, more or less, it is up to us to explore.
So while I stand behind my original thought processes of 'don't spend time doing anything that doesn't produce definable and easy to identify results or anything you can't test for,' I think we should leave room for the trail blazers who are willing to spend their time and money on their tanks at home attempting to further the conversation and our knowledge. In this specific case, there is one thing we all know for sure: Natural sea water produces results. This is the environment corals evolved to thrive in, so attempting to emulate that certainly isn't a bad concept. That said, I can tell you it's almost certainly the most expensive and time-consuming concept and the reason why most reefers probably won't value the results enough to do it.
Bringing this all the way back to eliminating maintenance water changes and the impact on trace elements, I guess I would be pretty nervous about the presumably ever decreasing levels. While water changes do replenish some amount of trace elements, they are far from the most efficient or effective way of doing so. If I attempted near zero water changes, I would see a lot of value in testing periodically to see what is being depleted and by how much. At a minimum, I think I would select a method of calcium and alkalinity replenishment which is likely to replenish some amount of minor or trace elements. Potentially, I would even explore a calcium reactor which theoretically replenishes many elements and, long term, can be much more cost effective than other approaches.
