First off, congratulations on a well-run tank, Chris. If you don't mind sharing, could you mention your existing filtration, feeding habits and observed coral growth? I have a skimmer, and an algae scrubber. Similar to you, I rarely turn my skimmer on, and am genuinely curious about alternate ways of reef maintenance.
That being said, one of the things that may warrant a skimmer is if you want to feed your tankmates (corals and fish) more than what you currently are with the expectation of higher growth rates, better coloration etc, then a skimmer may help bridge the gap until the other parts of your filtration system catches up to the increased nutrient intake.
Overall, I totally am in agreement with you, and prefer biological methods of keeping my tank healthy and happy.
Of course! My tank is a 20 gallon long (80 litres) filtered by an oversized canister containing about 4 kg of biomedia. I have an inline prefilter on the inlet that contains filter floss/sponges, which I clean and change weekly. This means the canister itself is essentially a nitrate reactor that I only have to open and clean every 6 months or so. On the outlet, I have a media reactor that I've turned into a DIY algae reactor. This was to help control PO4 – beyond the initial cycle, NO3 was always stable at 5ppm, though it's had the effect of reducing my NO3 to < 1ppm as well. You can see some pictures of this and further explanation in my build thread.
I feed pretty heavily, usually flake in the morning for the fish, then in the evening close to lights out, I feed a DIY frozen food based on the DIY BRS reef chili (contains reef roids, LPS pellets, vitamins, selcon, mysis, red phytoplankton, rotifers, lobster eggs, mysis, prawn, tuna, copepods etc). I also add amino acids daily at the same time.
I perform 10% weekly water changes and siphon the sand bed.
I currently have a bit of an issue with overall slow growth on my soft corals and LPS, and the few SPS being generally a bit unhappy and some have shown RTN. I also have only tiny amounts of coraline growth. The system is still young (about 10 months?) so it could well be too soon for SPS, but I've had a birds nest that was growing really well since I added it around the 2 months mark but just recently started showing some necrosis. I also started to get coraline on the glass and then it stopped. I can trace back the start of my problems to when I added a Chinese black box light that I think just doesn't have the spectrum it advertised (the 420 LEDs look more like they're 450-60, i.e. no hint of violet to them). The PAR is also pretty low unless I crank up the whites, which looks awful. I have recently ordered some reefbreeder photons that I hope will help, though it could also be my low nutrients.
These issues are in part why I am considering a skimmer as I read over and over how essential they are for SPS. This is why I wanted to know what I am missing by not having one, so I can understand if a skimmer would help in my case. The impression so far though is that it wouldn't add much beyond some redundancy? The reefdudes stream above also mentioned that they probably aren't worth it on nanos.
It's interesting to hear you have yours off most the time!