RBurke is right about the reduction in back pressure with these new membrane diffusers. Sue is correct on the pressure requirement on reaching the deeper depths of your pond. You will not be happy with the performance of your 1/4hp if you desire to go that deep.
Like Sue mentioned, to reduce the chance of warming your pond too much to hold trout, you may want to place the diffuser in a more shallow location. If you keep it at the 10 foot level, you can use your 1/4hp. Are you at any elevation?
Generally, trout require water colder than 68. Another option to help keep it cool but aerated is to as mentioned aerate at night but add a surface aerator along with the bottom system. This surface aerator will act as a cooling tower at night when the water is thrown into the air. The bottom diffuser will eventually bring it to the lower levels of the pond.
Lastly, without a doubt, use self-weighted tubing. Save yourself the headaches and problems associated with non-weighted tubing.
