Why is my mixers send output so quiet?

There is a gain control next to the meter for "Return" level. Do you have that full up?
Do you have the cables/plugs wired as required to suit the equipment at both ends?

Try putting a cable directly from effects send to effects return(L) - if you can get full level then, the problem is somewhere in the pedals or the connections between them.

If the level is bad with just that cable, either the cable or mixer is faulty..

Read

The

Owner's

Manual

And

Learn

How

To

Make

Necessary

Adjustments.

Another thing to try is do not use the AUX return...plug the output of the pedal directly to to the 1/4 inch LINE input on any spare input channel. Adjust the GAIN knob up until you are getting plenty of signal from the pedal. Then turn up the LEVEL knob on that channel until you hear the effect. That will work and should give you plenty of effects on your mic.

Check to see if your AUX loop has a separate channel fader. It might be turned down a bit too much.

Without knowing the first things about what YOU own, and how you have connected it, I would say that it is either a mike power issue (battery? Phantom power/ What?) or a pre-amp issue. Or just plain LEVEL. I am hardly an expert in THIS area, but know enough to make MY equipment work well.