yes...closed system works very well as long as you provide a filter bag over the inlet pipe and change it now and again. This way the bio-media wont clog...or of course you can filter the water first and then run it through your tower...either way works. One thing with a closed system you have to watch. Put a valve on the intake side so that you can adjust the amount of water in the bottom of the tower to prevent the return pump from running dry. (unnecessary if it dumps directly into a sump or even the tank.)
Basicly the same way that you do a bio-tower but you run into the age old water distribution problem...Basicly keeping all of the bio-media in a 55 gallon drum wet. Drip trays and other methouds clog fairly quickly as do sprinkler heads. Strangely enough the best way I found (from building pond filters) is to have the outlet pipe possitioned over a flattish rock laying on some eggcrate over the media...of all things...the random splashing and dripping covers all the media and can't clog.
I just looked up 12 and 18in clear diam pvc and it is like $110 a foot. Anyone know where I can get it cheaper, or do I just have to use white. How do you get the eggcrate a few inches off the bottom if the bottom is caped?
cut and glue in the eggcrate before capping the pipe. Leave a good foot or so clear of media at the bottom. You don't need clear pipe...Rally mentioned having some and I said I thaught it would be cool but I'd never pay that much for it...