Congrats on taking your pond to the next level! You've gotten great advice above, and it sounds like you've done your homework too. Your thoughts on running at 8-10ft of a 15ft hole are good, there's been much discussion here on maintaining some sort of a thermocline as a refuge.
I run the same pump as you and will comment on that, it will easily perform at that depth. Since you haven't installed it yet, it's noteworthy to mention that it will easily run 3 of the Matalas also. The variables to keep in mind are, the length of your runs, and hose diameter. Bigger is better here, I recommend using 3/4" lines. Also, to have even flow at the various depths/distances, a valve station, where the lines branch somewhere near the waters edge is a good idea.
What I have ordered is a Hiblow 120LL, 200 ft. of 1/2" weighted hose and two 12" Matala diffusers that I will have to build mounts for. I was planning on running 100 ft. of hose out and then Tee'ing it off to two separate 50' hoses out to the diffusers, one will go towards the deep and the other towards a shallower bank. I wasn't sure if I could use more than two diffusers with this set up. I'd love to be able to add a third one if I wouldn't lose functionality of the system with it.
