Ok, we have established what a refugium is and how it should be connected to the balance of your existing system. We have seen why it's important to consider the right plumbing and to plan accordingly. Now let's discuss what to place inside, preparatory to introducing our animal load.
I favor live sand and some live rock work. Since primary filtration is NOT an issue, the aesthetics of your creation take priority. I would recommend a sand bed at least 1-1/2 inches deep, 2 inches being better. 10 gallon aquariums aren't all that deep so you will have to judge the sand thing for yourself. My idea when erecting my first refugium was to establish an area for natural denitrification. This aids both tanks being linked to a common water source and a deeper sand bed makes this possible. I used live aragonite sand, mail ordered from AquaCon in Florida. However, there are many sources for sand, as well as live rock. The few pieces of rock rubble that I used came from my main tank...plenty to go around. Once again, if using the main tank's filtration, biological considerations are not necessary.
What about lighting? I have seen a few ideas that allow light to be redirected over the refugiums but they were stop-gap measures. Better to have a proprietary lighting system designed strictly for the refugium. A 6500K and a mono-phosphor 7100K blue provide nice lighting for a tank this size. I recommend Energy Savers Unlimited (ESU) Coralife bulbs, or similar OSRAM lighting. These are ideal units that feature twin OSRAM fluorescent bulbs in a neat aluminum reflector. By shallowing the water column, via the sand bed, these OSRAMS will give the intensity needed for your refugium inhabitants. Being just 9 watts each, they radiate at a 75 watt, incandescent level! That's equal to 150 watts of incandescent light on a 10 gallon tank! Plenty of beneficial illumination. I used egg crate cut to the inside dimensions of the tank frame and simply placed the reflector on this. Instant light hood! The reflector keeps stray light out of your eyes and keeps the rest of the room comfortable.
In conclusion, all we are striving for here is to provide a safe and quiet haven for our animals to flourish. I allowed caulerpas to grow, and even cultured some halimeda algaes as well! I placed two Garden Eels in my original setup. Did you know they were EXCELLENT jumpers?
From more information about refugiums, how to set one up, the various types of set ups you can choose and how to build one, refer to our Refugium Set Up Resources.
Best of luck in your refugium endeavors!