I don’t have my own camera yet so all pictures have to come from borrowing one. However, I do have some pictures of a couple zero-water change tanks at my dad’s house. The 40 gal reef is filtered by caluerpa growing in the tank and has had zero water changes for about 5 years now. The 70 gal reef is filtered by an ATS I designed and built and has never had a water change. It is about 1 year old now.
In general skimmers are detrimental to reef tanks that are naturally filtered by plant growth, despite their widespread popularity. Lower nutrient levels are achieved by algae based filtration than are ever possible with a skimmer. Skimmers remove the plankton that is the base of the reef food chain. They take out the natural food of corals and remove the larval forms of most reef creatures. However, bladed pumps already kill 90% of your plankton. So unless you use a bladeless method for circulation removing the skimmer won’t get you anywhere near natural plankton levels. Non-plankton killing methods would include bladeless pumps (see discflo.com), air lift, some wave makers, Archimedes screws, some large, slow-moving volumetric piston pumps, etc.
It is possible to setup the perfect no maintenance situation (no feeding, no harvesting, little micro-algae growth in the tank, long term) in a small box. But you must seal it air tight and have some portion of the system always lighted. Without harvesting of algae the algae will continue to increase indefinitely by removing nutrients from the air if you don’t make it completely self-contained.
Since there is no air being pumped in at night, you must always have light unless the system is mostly plants. You could risk the running out of oxygen and accept the chemical instability of the day-night pH swing, but it’s better to have some portion always lighted. Also the stocking levels will have to be low since there is no outside source of nutrients.
With large nutrient export via plants very heavy stocking is possible with no water changes. I kept a 20 gal reef very heavily stocked and fed for about 8 months filtered with a 10 gal caulerpa refugium. I fed heavily 3 times a day frozen, flake and pellet foods. This included 12 green chromis, 3 blue yellow tail damsels, 1 four-stripe damsel, 1 domino damsel, 1 kole tang, 1 convict tang, 1 yellow tang, 1 falco hawkfish, 2 chalk basslets, 1 royal gramma, 1 six-line wrasse, 1 atlantic pygmy angel, 2 large Hawaiian hermits, 5 red reef hermits, 12 blue reef hermits, 2 emerald crabs, 3 peppermint shrimp, and 1 skunk cleaner shrimp. On ATS filtered fish farms densities of over 1 lb of fish per gallon are achieved for tilapia.
I think most people will be happier with feeding and nutrient export rather than a closed system, but the completely closed system is an interesting challenge.
My experience is that any fish only tank with normal stocking density will be adequately filtered by simply providing good lighting and including plants the fish do not eat or destroy. Unless you have anemone-like creatures no other filtration is ever needed, and most soft coral will live, grow, and reproduce without anything being done besides letting some micro-algae grow in the tank. The preceding paragraph presumes no water changes.
Now, I am making some implicit assumptions in what I said. So let it be understood that I am including excellent quality live rock (already full of live adult detrivores of every description). For fish only tanks I have found that this is not necessary, but for coral you can’t just wait for bacteria to break down uneaten food and excrement. Bristle worms are probably the most important contributors, but ideally you want a wide diversity of mouth sizes and appetites.
