Koelsch will clear by itself. I usually add a bit of gelatin to help it along, but beyond that it just takes time... Koelsch is also one of very few beers I secondary to speed the process up a little bit.
My standard Koelsch fermentation looks something like this:
2 weeks primary starting at 64 degrees, ramping up to 70 degrees as activity slows.
Rack to secondary onto gelatin. Cool secondary as far down as is feasible (usually 40-45 degrees for me), and keep it there for 10-14 days.
Then bulk condition at room temperature (about 75-78 degrees for me) until transparent (i.e. you can see the yeast bed in the middle of the Better Bottle clearly when shining a flashlight through the bottle - usually another 1-3 weeks). Then bottle.
If you have the ability to keep the secondary cold for the entire conditioning phase, by all means do that instead of going back up to room temperature - it'll work faster that way.
If your Koelsch stays cloudy, it's a matter of recipe or process (i.e. using wheat malt, not achieving complete conversion, too much protein, etc).