Thanks for the vote of confidence,
Deadeye
, but you should be thankful that you haven't gained as much experience in this area as perhaps some of us older guys have. I'm referring specifically to the experience of having tried numerous dumb ideas that have resulted in killing or nearly killing our fish.
The Masked Shadow
, I find that a really useful tool when keeping outdoor stock tanks is a remote-reading laser thermometer. You can point it at the side of the tank at any water level...right at the top, right at the bottom, or anywhere in between...and instantly get an easy reading of the relative temperatures at those levels. I'm sure its not 100% accurate, as you are of course measuring the temperature of the poly tank surface itself, but I think it's pretty analogous to the water inside at that level. In order to minimize inaccuracy, I do it on the shaded side of the tank; the dot is pretty much invisible in direct sun anyways.
I'm not saying you should forego aeration altogether, for obvious reasons. Just be aware of the potential problem it can create with regards to temperature stratification, or a lack thereof, in the stock tank.