I take it's a bicube? I think I'm going to for the single mp40 right now. After reading and doing math out the mp40 is better option in the start. Mp10 I would need to run at around 80% each to get all water moving I think I the cube. This is bare bottom so I do not need to worry about sand issues. Also with the glass being 3/8s thick I was told the unit in reef crest might vibrate around due to the fact the pump can go from 0-100% output. At 100% power I think it will walk. Besides in a couple months prob 3 I will add the second 40 in
My tank 36" x 12" x 18". My aquascape is setup as a wall/island towards the middle of the tank with archways and lots of open nooks and crannies for coral, fish, crabs and shrimp and at least 3 inches between the rear and side walls.
I had the MP10es set up on the right tank wall for almost 2 months but I was not pleased with a couple thing. My overflow is setup on the side of the tank on the same wall as the MP10es. Though there was circulation throughout the tank, the bulk of the water power was near that MP10. The current would slow down along the opposite side of the tank and then hit the wall before going around the rockwall and along the rear of the tank before returning back to the MP10es.
My thinking was that this would also send the surface area around towards the skimmer for my overflow too. What was happening was the current was not strong on that other side of the tank to push enough/equal flow around my rockwork. I had pockets of flow that was too slow, and I didn't want too much resting water in the archways. Detritus, junk, etc. would collect in these areas and my fish would tend to stay on the side of the tank opposite of the MP10es.
I bought a new MP10Wes and the RF Module for the MO10es that I purchased new in Dec 2011. I was told that one would be enough for my tank and since I didn't have another, there was no need for a wireless module. Now that I have two MP10Wes working my tank, the flow is even on all sides in reefcrest mode, detritus stays suspended and in the water column and all of my fish use both sides of the tank. The surface of the water is always clear and I don't have to see that dusty collection of scum on the opposite side of the tank since the water current spins the entire surface area right into my overflow's skimmer. I don't run my MP10s at the same speed as I did before either, since it takes less power to move all of the water in the tank with power on both sides. My tank and I am very happy now.
With two pumps, the power from both sides of the tank are working evenly and together. With one, it takes more effort to reach the other side of that cube with all that churn on the side of the powerhead. My babies didn't like that churn, nor did my coral. And my pumps are quieter at the slower speed. I say do 2 MP10s or 2 MP40s. Whichever you can afford. And if you ever decide to upgrade from MP10s to MP40s, there are a lot hungry folks on these boards who would be happy to buy your used MP10s. You won't have any trouble selling them.