I have an EV240 w/Mag 18 on my 125gal. Running it externally too. Yea, during the break-in stage, just give it time. I know it seemed like a bit before the foam tower started to build. Also don't worry if you happen to see the foam tower collapse either. It seems almost anything can cause it, food in the water, your hand/arm in the water, and even the air changing in the room. Should always come back though. Startup settings, I'd say about 1/2 on the air valve and work your way open. The gate valve is pretty something your going to have to adjust to get the water level exactly perfect.
Be prepared for a good bit of maintenance though. I always seem to have to clean the neck every 3-5 days.