A CS 6-1 is 6" in diameter and a 5-3 is 5" in diameter.....
The CS Series are hand crafted with premium cast acrylic tube and vacuum formed parts along with 3/8" thick PVC Sheet material and custom PVC parts which are welded together with sophisticated hot air welding technology.
The RS Series protein skimmers are the latest addition to the peerless line of Euro-Reef products. These skimmers are fabricated with the highest quality cell cast sheet and tube material in combination with custom designed and formed plastics. Identical in design and performance to the world famous CS Series, the RS Series has established a new benchmark for quality, performance and price all in one unit
The primary difference is that the CS Series are hand crafted with cell cast acrylic tube and are welded to 3/8" PVC plate while the ES Series protein skimmers are hand crafted with extruded acrylic tube and glued to cell cast acrylic sheet material.
The ASM skimmers are an excellant alternative to euro-reef... from everything i've been told they work just as well and are a lot cheaper.......
www.roesmarineworld.com has the best prices on asm skimmers that i've found....