.. first of all, try it without the pedals in the loop. Maybe this is is where your problem starts. I've had also problems with some pedals, for example the Visual Sound H2o chorus/delay pedal. This pedal is really great, but not so great in the fx loop of the ace when the amp is cranked. It sounds weird, like there's a signal overload goes into the pedal, which the pedal cannot handle..
Channel one, the channel you're talking about, is more sensitive for this problem, because the volume of this channel is (in general) set higher than the channel master of channel 2, ... to compensate the volume differences of the channels..
but... if this is also your problem: 2 solutions.
1, lower the channel masters, not above 10 o clock ..
2, sell the pedal(s) and buy another one that can handle the signal.. (this is what I did. problem solved!)
good luck!