I just added a 2nd MP10w on my 34g cube. always thought 2 would be too much.
but i am very happy
my tank is almost exactly one year old. Ive had one MP10w this whole time and my tank looked good. just recently added SPS and I needed more flow. I added some Koralia nanos, attached them to my RKE on wavemaker. the flow was decent but i had issues with noise and the violence of the hard stops and starts.
took them out and added an MP10w to opposite side of tank. spent a few hours messing with placement.
my tank looks very happy. my LPS are actually loving it, i didn't expect that but the more random flow from the two MP10's on reefcrest mode is just beautiful!! basically the whole tank is happy. my fish are even happier those clicking koralias are gone lol...
you just have to balance the flow with 2 in a small tank. i the master pump down a notch or two.