Chuck,
Bill Cody was right on the money about the trout. It's like this: A typical pond no matter how deep it is, is not made for trout unless you have a cold climate or you are doing something to bring the water temps down. Optimum temps are 55 to 65 F., and in those temps they need at least 5 ppms. Once your water gets to 70 to the low 70's they will become stressed and death will not be far off.
I run aerated well water into my small deep ponds to keep the water cool enough. Deep cold water is only part of the equation. It has to have enough oxygen too. Most ponds that stratify have low D.O. in the deeper water (at least to low for trout). If you use a diffuser(s) you make the water temp essentially the same from top to bottom and in summer it would probaby go at least into the 70's. That's too warm for trout. Catch 22.
I hate to sound cynical but I don't see the point in the D.O. meter unless you want to keep a log or something. If D.O. gets low there's nothing you can really do about it, and it typically means you did something terribly wrong anyway. So the D.0. meter is going to show you yes I screwed up but, if you prevented any bad water quality in the beginning you shouldn't have to worry about it or need a D.O. meter.
Typically only fish farmers monitor D.O. levels as they are pushing their carrying capacities to the limit. As a recreational ponder you shouldn't be anywhere near that.
