Pond Boss Forums INTRO Questions & Observations how do you sample bottom waters?

I've been reading about aeration and shutting the pump after the fall overturn and re-starting it in spring before the bottom waters drop below 3 ppm DO levels. Well my pond is over 20 feet deep and the thermocline forms at over 10 feet, so what's a convenient way to sample bottom water. Also who makes or sells analytical kits for DO testing. It would be interesting to test through the seasons and see the variations in DO. And also judge the effectiveness of the aeration system and bubbler placement.