Be glad to do my best. Closed loop is a circulation system that does not filter water. It has a pump that draws water from the tank and pumps it back in through various inlets. Sometimes using lock lines, or a switching ball valve, or a ocean motion 4 or 8 way outlet system. It helps to increase water flow in the tank.
A sump is a system under the tank that holds water to be filtered. It can be a glass tank, or acrylic, or a rubbermaid tub or any thing inert that will hold water. People put thier heaters, skimmers, filter media, uv sterilizers, and whatever else they want in the sump so it is invisible, and in a central location. It also because of the overflows in the tank keeps the water level in the tank stable and lets you drip your makeup water or kalkwasser out of sight.
Kalkwasser is lime in reverse osmosis water that is driped into the tank to replace the calcium and carbonate hardness buffer that is used by the corals and the acids of metabolizim in the tank.
A kalkreactor does the same thing just a little better
A refugium is a small or large tank in line with the main system without predetors having a either or a combination of , algae, live rock, or live sand, it is a place to let benifiacal small critters grow away from hungry mouths and can be a place to grow algae for nutrient export ( ie trim the algae and throw it away removing the waste products that fed the algae in the first place)
HTH you in some way. Steve
