sanababit: I dont see where you mentioned your nitrite level, and are those coils 1/4"OD or ID if its ID then the output of a stream its too fast for starting out. a 5ppm drop now sounds like a start.
mwood: actually at first it will create nitrate not a whole lot and not more than any other large surface area in your tank, but its still more than you had. and while cycling you dont need no nitrites in the output you just want very little nitrites in the output try not to micromanage it IE test every 3 days instead of 3x a day....
the amount of time it takes these to cycle is only a guess, its just like when you cycled your main tank you can do things to speed up the cycle (borrow from others, feed heavily, adjust flow more frequently ....) ((((NOTE that was adjust not speedup or slow down you have to test not guess )))) and you can do things that slow down the cycle (empty the unit, run it with no ammonia/nitrite/nitrate). the 4 to 6 week estimate is just that an estimate. NOW with that you should see some form of droping nitrate fairly quickly its just how much and does it hold that you cant count on.
cb747: 4" pipe is expensive maybe 2" pipe instead use as much pipe as you need to keep the coils under control
it really doesnt take that much you just need to slow down the flow for a little...