I'm unsure about browns. ... Can I really stock splake? I didn't know people sold them.
How do I find out bottom temperatures?
I'd advise against Browns. My experience with them in small, stocked BOW's in Wisconsin is that they are very wary and difficult to catch on spinners/spoons. Minnows seem to work OK as bait, and tiny dry flies might do the trick, but Browns are a tough fish. They can also get large and very piscivorous. If you want another large-sized aggressive predator in your pond to supplement the SMB, stocking Walleye or just paying through the nose for large Brooks from a hatchery might be the ticket.
I don't know if people sell Splake, but I know that the Maine DNR loves them. I'm not sure of temperature tolerance, it'd be neat to throw 3-4 in and see if they come back out. They're supposed to grow quite quickly.
Best technique for bottom temperature that I know of is to put a waterproof thermometer in a jar full of water, tie a string around the jar, and throw it into a deep part of the pond. Give it 12 hours, then haul it up and read the temperature. The jar of water will not change temperature quickly, so you can get an accurate reading of the bottom.
