Thanks for the kind words.
Let me just clarify my thoughts on overskimming if we want to go into details. There are lots of things skimmers do, and people obviously have great tanks with no skimming, so I think arguments about skimming could range from none to huge amounts, what is best? There certainly are some situations where some aspects of skimming might be a negative, even if other aspects in the same tank are a positive, and only the aquarist can decide what is a net benefit.
Among the many things skimmers do is aerate (especially important for CO2 and O2). I would run a skimmer for that purpose alone, and in my tank, when I experimented with no skimming, the pH went too high (I used limewater) and I did not prefer the pH range that resulted. In my situation, too much aeration is not a real probability.
But in some tanks in a high CO2 home environment, it might actually be best to not aerate during the peak hours of the day, and to let photosynthesis carry the pH upwards from the low level that might be attained if the water was in perfect equilibrium with the air. Studies have shown that even a short pH peak can help corals relative to spending all their time at low pH. So in this case, no skimming or less skimming during the day could be a net plus.
Another thing that skimmers do is remove organics. Some may be toxins that have no real positive benefit, so good riddence. Others may be materials that corals, or other organisms could consume. They may also be food for bacteria that in turn can become food for other organisms. Organics have a myriad of effects, from "bad" to "good". Is removing organics overall a benefit? Is too much removal bad? This topic alone could be discussed endlessly. I believe that removing organics overall and then adding back specific ones that you think are beneficial (if any are needed; these might be amino acids, vinegar, vodka, fatty acids, foods in general, etc.; lots of possibilities) may be a better plan than just accepting what organics are naturally present, but again, that's debatable and others may choose different methods. So skimming and more skimming might be debated as to the benefit in this regard.
Another thing that skimmers do is remove N, P, and a mix of trace elements (such a copper and iron) that are part of, or bound to, organics that get skimmed out. Whether that export is desirable or undesirable, and whether it can be overdone depends entirely on the tank and whether it has too much, just enough, or too little of each and every one of those components. A heavily skimmed tank might need more of certain trace elements or inorganic nutrients (or foods) to maintain enough of them when a lighter skimmed tank might need less. Having a constant export of these things (by skimming, macroalgae, etc.) that you then add back just what you want or need is the essence of high testing methods like Triton, but I recognize they are a lot of work and expense and may not be everyone's cup of tea. If you are not monitoring closely, it might be possible to under or over skim, depending on what you consider to be the most important thing to gauge whether you are doing one or the other. If you monitor sufficiently, overskimming may not be a concern.
You mentioned bacteria, and certainly skimmers can remove some bacteria. Is that beneficial? Not sure. It may depend on the tank. Can you remove too much? Again, I'm not sure. In both cases the answer may depend on what criteria is being used to determine whether the bacteria and their export are a benefit or a detriment. I do think it is relatively easy to boost bacteria by organic carbon dosing, if not by other means. Despite having a decent (not super) skimmer, I could easily dose enough vinegar to make the water cloudy with microoorganisms. That might be a benefit for feeding filter feeders, and might be a good nutrient control mechanism. Skimming them out may have benefits (N and P export from the tank system) or detriments (reduced feeding potential, too low of N and P, etc.).
All of these things a skimmer might do represent a balance. I think that regardless of the extent of skimming (within reason), I could attain a good balance of all of these in a reef tank with appropriate foods, dosing, etc. Does that mean it is the best way to attain that balance? Not sure. I'm not even sure that all reefers identify "best" the same way (time, cost, results only, etc.) Might attaining this balance be easier with lesser skimming? Maybe with no skimming? Maybe. Maybe.
I think there are loads of possibilities for reef tank husbandry, and the question of overskimming being bad may not have a single "true" answer.
Is it possible to overskim? Well, certainly yes in some scenarios. Too much skimming could be undesirable in some situations or times of the day.
Can the same positive results be attained in a tank with a lot of skimming and appropriate "other" measures, compared to lesser skimming in that tank and different "other" measures? Probably yes.
Which is "best"? I'm not sure. I'm not even sure there is a single answer that folks would agree on after seeing the results.
