That is a beautiful stand! Their is really no cheap or reasonable way to have a display refugium unless the high water level (overflow level) of your refugium is above the water top surface level of your main display tank. If the level of the refugium is below that level you would need to pump the water up to your main tanks top. With the refugium sitting on the table shown you would essentially have the same thing as a refugium inside your cabinet (equipment and cost wise anyway). The only difference would be its visibility. I doubt you would be pleased with a refugiums equipment being so much in site in said arrangement. If you do have enough room under your tank in the cabinet you would probably prefer it aesthetically as nearly ever thing would be hidden behind the tank and within the stand. You would be able to see the top of a siphon overflow unit and its skimmer box inside of the main tank, but they, in general, are usually considered more acceptable to look at than tubes, hoses or piping in most peoples opinions. The least obtrusive method of plumbing water to a tank below your main tank is through a hole that would have to be drilled in your tank wall. This is easy and inexpensive, but should really be done to an empty tank. If overall you are considering aesthetics important you will probably want to put your heater(s) and other accessories below your display tank also. If that is the case you will want to make a combination sump/refugium. This is simple to do. You would remove water from your main tank through a siphon mechanism or through an overflow bulkhead. Before the drain pipe reached the tank below you would split the flow so that a small portion of your water went inti your refugium. The water from this would overflow a partition into your sumo where the main flow from your tank drains. the combined water would overflow a second partition int a return chamber where a pump would pull water to be pumped back up to pump. I do not remember what you wanted to keep in your tank, but assuming it is principally live rock and fish, means even a 10 gallon tank would be adequate for a pump large enough to provide all the circulation flow your tank would need. So you would not even have to look at power head pumps, if you choose not to. If your intent is to keep coral I would advise you get a protein skimmer. This would make for a small refugium if you put the skimmer in the refugium/sump tank but a skimmer in general is much more capable of handling large fish and coral loads and inexperience reef keepers. Coral tanks are kept by some home aquarists with success but your really limited in what you can and cannot keep and you have to keep the amounts of fish to a small amount and feed very sparingly and be real good about doing water changes. A skimmer is usually a higher priority with more people than a refugium which is why I speak of a refugium/sump combination. Typical installations for sumps and sump/refugiums is the largest size tank you can fit in your stand. I do not mean to discourage you, but just let you know it is a procedure that should be well thought out and planned. Impulsiveness in the marine/reef trade you later means spending money to replace spur of the moment measures, and/or settling for less than you really desire or need. You might check out wet web media, as another source of good material. It is a much larger site with much more material. It is a colder less personal site but the site monitors answer all questions, supply articles and are all known writers and researchers in the marine and reef aquarium trade. You do have to go through a lot of material to extract the information you want, but questions will be answered that you never even would think to have asked. The least amount of pipe you could possibly have showing betwween the two tanks would be two pipes. One out the back of your display tank and across to the top of the near side of the refugium tank. You would need a second pipe to come out ot the top rear of thr refugium where it can drop down and then run behind the back of the tank across to behind the display tank where it would then rise up to run over the back of the tank and into the water. In an under the stand tank you would just see the overflow, as in the other set up, and end of the pipe run going into the tank. Everything else would be behind the tank or within the tank stand. Now this is long winded. Like a Wet Web right up.
