Ditto for me (upgrading to the MJ 1200) and have generally been pretty happy w/ it. It does require some tweaking from time to time but has produced more flow back into the tank as well as more foam. If I recall correctly the venturi modification kit's available from Premium Aquatics for something around $3-4.00.
hth
Dunno if this applies to all concerned, but I have one of the earlier models of the CPR MRT (micro reef tank), which has the BakPak strapped on to the tank. The standard venturi mod on a Maxi-jet 1220 will not fit. I found that simply inserting the end of the air hose into the powerhead intake works fine though. Even if you don't purchase a venturi attachemnt, you will still want to deaden the noise of the airflow on the end of your venturi hose.
Added via edit-
Be careful not to upgrade to too large of a pump- the increased flow may decrease your contact time significantly, thereby lowering the efficiency of the skimmer.
[ September 19, 2001: Message edited by: Chucker ]
I switched to a Maxi Jet 900 and hated it. Ended up putting the Rio back on. The bubbles are not as "micro" in my opinion. And the chug chug dove me crazy.
It should be a straight swap. I tried a maxijet 1200 w/venturi on my bakpak and eventually put the Rio back on. I suspected I wasn't getting as fine bubbles and had too high of a flow through rate. 900 might work better. It works ok though, results probably vary. I wondered if anyone had tried a bigger Rio with recirc. venturi?