Don't be sorry for asking a lot of questions. It's the right thing to do, so ask away
I have an 18 gallon mini reef that's been up and running for four years successsfully. The following is what the tank has (you can read it also in my profile as well as see pictures of this tank in my gallery). Though I'll type it out here also...
Ecosystem 40 refegium, at least 3" of aragonite/live sand substrate, lots of live rock, a heater and a double power compact light...one daylight; one actinic. Very simple set up.
It is not recommended to use any kind of freshwater gravel because of the excess silicates which can contribute to a serious algae outbreak. Aragonite topped with live sand is best. When putting the system together, you want to put in the bottom pieces of rock before the substrate so the substrate can help provide a sturdy foundation for the rock work. I live in California so this is always in mind cause the ground is always moving here.
The Ecosystem 40 refugium takes up the entire back portion of the tank so there's no room at all for any additional filtration, but it's not needed. The refugium alone has done great and the live rock is the natural bio filtering 'unit'. I find refugiums have advantages over protein skimmers. You would need one or the other. Some people use both, but in a ten gallon, needless to get into that kind of expense. My tank has done so well to even support an infant Imperator angel till she got too big. Not an easy critter to keep alive so fat and happy. She had all kinds of sponges and natural growth in there to graze on.
I have found that refugiums help promote some nice microfauna that isn't gotten by the protein skimmer. The difference between them is that protein skimmers mechanically remove proteins from the water by the use of tiny bubbles for the proteins to ride up into the collection cup. A refugium however, this protein is biologically utilized and broken down, so the return water has a different chemistry than the return water from a protein skimmer. It provides a fully functioning biological system.
Having a deep sandbed and critters that live and crawl in the sand will help keep nitrates down by providing an oxygen free area in the environment for nitrate eating bacteria to cultivate. The animals in the sandbed are needed to release any trapped hydrogen gases from this process. The deeper the substrate, the heavier th layers of sand on top of the bottom layers to choke it of oxygen.
You won't really be able to vaccuum the substrate for waste so you need to build the system to where it can help itself for the most part.
My little 18 gets a basic routine maintenance of 15% water change once every two weeks. Calcium and alkalinity are added when needed. The tank gets fed every few days with a mix of flake, veggie matter, cyclopse and phytoplankton. It pretty much provides most of the nutrition the critters need naturally in between feeds with algae, copepods, and fish poop. Corals eat fish poop.
Temperature of a marine tank should be stable at 76 degrees. Set the tank up where it will not recieve any light from your windows and far away from drafts. Perferrably up against a wall that doesn't have the outside on the other side of the wall (to help keep temps from fluctuating). Temperature stability is perhaps the most important element to provide in a marine tank. Unlike freshwater fish who are adapted to changes, marine fish are not due to the sheer vastness of the oceans they come from. The oceans experience very little change in the waters condition. Lakes, streams, rivers and such are always experiencing changes and therefore freshwater fish are naturally adapted to withstand changes in their environments. This is the very reason why marine animals are harder to keep alive in captivity. This also includes the basic water parameters of pH, ammonia, nitrite and nitrate. A reef tank with coral would not survive well with nitrates over 10ppm. They start to wilt or slime up. Building a stable environment from the very beginning will help avoid many of the common problems people face with their marine tanks.
Also a must is a quarantine tank to put your newly purchased fish into for a week or two to make sure it doesn't come down with anything that can upset or destroy the system. A simple small five gallon tank with a sponge filter, heater, and something for the animal to hide in. No substrate and can use basic lighting.
Salinity or SG
for a marine tank is between 1.020 and 1.025. I keep any tanks with coral at 1.024 to 1.025, but not any higher. Corals like the higher salinity, but too high can harm the fish. An important thing to have on hand at all times is freshwater to top off the tank when the tank water evaporates. The salt doesn't evaporate with the water so salinity goes up. Adding freshwater will bring the salinity back down.
Any other questions you'd like to throw at us??? Fire away!!