I take flak for this fairly often when I mention it, but I have a lot of research and more than 2.5 years into the experiment all seems well... so...here's my confession:
I do maybe 2 or 3 water changes a year on my tank. Longest I've let it go was 9 months, and I didn't see any problems, just felt that with salt creep and ATO I might start to see salinity problems.
My intent with marine aquariums is to produce a near self sustaining ecosystem, so I seek to incorporate as much of the natural processes from a reef as I can. My tank is the result of about 6 months of reading up on how to make a natural reef aquarium, and what has and what hasn't worked. It's been doing good for over 2.5 years now, *knock on wood* and takes _VERY_ little work to keep it running smooth. I would say maybe 2 hours a month.
My take is this:
#1 important aspect is biodiversity. I've snorkeled and dived enough to know that there's no such thing as an SPS or LPS or NPS etc. _ONLY_ reef anywhere in the world. There are large areas of reef that may have only one dominant species to the exclusion of ALL other species for many square yards...but as a whole ecosystem, reefs are among the most biodiverse ecosystems on the planet - strive for that in miniature.
Bioload is the next most important aspect. I don't feel there's an upper limit to the numbers and size of most SPS you can keep, but many LPS and essentially all NPS and softies have much more active metabolisms for their size, and their waste products need to be considered, especially the non photo synthetics that require targeted feeding or for those who opt (as I do) to feed LPS and softies from time to time. Keeping your fish and other tank inhabitants well fed and happy is a good way to prevent loss and disease, but too many fish along with overfeeding and not enough export can kill off a tank, as we all know.... but I suspect not having enough fish and their associated nutrients (poop) can also damage, or at least limit, a healthy coral population. There's a fine balance, and in an ideally balanced tank, I suspect you could do away with ALL mechanical filtering, even protein skimming... but alas, 2 or 3 small fish in a 240 gallon tank is hard to define as natural, and probably isn't what we'd want anyways... so we have hardware to let us tune that balance a bit.
First in the hardware category is the living stuff...
Maricultured or otherwise sustainably harvested Live rock is ESSENTIAL. manufactured or dry base rock has value for aquascaping, building up a foundation, and helping with price... but I figure any tank I build in the future will contain at least 50% fresh wet live rock from reputable sellers.
A good medium to deep sand bed, dry and seeded with sand from an established and HEALTHY aquarium. Bare bottom tanks are fine for laboratories, fish sellers, QT, and some FO/species tanks, but they look horrible in a reef tank, and there's NOTHING natural about a bare bottom tank. Read up on anoxic bacteria and deep sand beds if you plan to go over 3" deep, but the deeper the better in terms of natural processes.
A refugium is a MUST. We cannot recreate the whole ocean in one go, so we have to isolate and replicate sections of it as we can. In nature there's a balance between the reproduction rates of microfauna and the metabolism and appetite of their predatory counterparts, which are in turn prey for larger and larger fish - so large we can't keep them. Without the larger predators, the smaller prey will quickly be depleted without a safe zone to thrive. This microfauna is the primary food source for many corals and fish species, without it corals wither away and die. Refugiums also offer a great place for a deep sand bed, macroalgae for organic nutrient uptake - but should NEVER be used as temporary holding for a fish or other predator.
Then we have mechanical filtration and devices to facilitate the natural actions of the rock and corals.
A good skimmer is essential. We don't have wave action to export organics/proteins and provide gas exchange so this is our next best thing, and honestly I think it's much more efficient that natural wave action for the scale anyways. Over skimming is a concern tho, since many tank inhabitants need the organic waste and proteins a skimmer removes. Clams, SPS, worms, and bacteria all feed on the "waste" from higher order life. When I got started I was told get a skimmer that will process at least double your tanks volume per hour... I don't think that's good advice for a properly balanced reef tank, but great if you keep too many fish, or any heavy eaters like puffers, sharks, lions, eels... basically, get a skimmer that will move around 1 to 1.5 tank volumes per hour. once mine broke in and started running smooth it produced a fairly dry, not too bad smelling, dark green glop.
Flow is vitally important. I lost a few sps early on. In part it was due to bad species selection, but now I consider flow was a MAJOR factor in their demise. I started out with just the return from the sump, and 2 smaller koralia's with no wave makers... just pointed more or less at each other... I've since upgraded to 2 Vortech MP40w's set on one of the built in ecotech modes... I think it's lagoon mode, not sure... at any rate, I got them for my 180, so in a 58g tank they're on the overkill side and I run them set to almost the lowest power setting... but the improvement in SPS growth was phenomenal. A (nearly true, pseudo-) random flow pattern makes a giant difference, and they really do keep particles suspended. I used to use a turkey baster to blast my rocks... now, nothing collects on them, and when I blast I get virtually nothing. It never settles, or when it does, it does so in places my blaster doesn't reach... which is fine, just like in nature
Finally, we have the dry side...
Lights play an important role of course - having enough of the right type. natural sun light's constant is 1361 watts per square meter on Earth, so calculate the area of the top of your tank, and figure it out from there. e.g. a 120g tank 48x24 on top, is ~.73 square meters, so you'd want about 993 watts of light. Lighting isn't 100% efficient, so figure anything over 1000 watts would start to approximate natural lighting, with 1250-1500 being closer to the actual natural illumination. For the 120g tank, that's 10w per gallon.... but you'd want the same light if the tank was 240 gallons, and twice as deep, or 60 gallons and half as deep... it's surface area that matters.
And finally, chemicals. Corals suck...calcium and carbonate from the water. One MAJOR reason water changes help tanks is that they reintroduce the major and trace elements corals and other invertebrates need to survive and thrive. But there's NO reason we must do water changes for this reason alone. Marine Biologists have a pretty solid grasp on what corals use, if not how they use it, and metabolism studies have shown what gets used up in what amounts by total systems as well... and wouldn't you know it, some of these researches have capitalized on their research and make products designed to promote growth in corals via regular dosing of the required elements. They're not really that much more expensive than quality salt, and I've noted major growth in corals when I am properly maintaining calcium and carbonate levels along with dosing small amounts of trace mineral products.
Anyways... I'm not sure how complete this post is as I've written over the course of a few hours as I'm doing other things... but moer or less it's just my log/notes of what I've been doing, things I think are key to my success with my tank, and what I do that allows me to put in minimal effort to keep the tank healthy. In over a year I've lost one coral, and 2 fish - none of which ever properly established in the first place. Everything I've put in that's lasted more than a month or two is still in there.
-Doug
