I have been experimenting a bit with hydroponics lately, and one of the important things when building a hydroponic system is to aerate the water/nutrient solution. This is usually performed with an ordinary air pump for aquariums by hobby hydroponic growers.
I know you can buy professional dissolved oxygen sensors, but these seem to be quite expensive.
My question is can you make or buy some simple sensor that can measure the amount of dissolved air in water?
The sensor does not have to precise in any way, or provide any absolute values. I just want to see some sensor value rise when I aerate the water, and fall slowly as the aeration dissipates (and is absorbed by the plants). This should be sufficient for regulating the aeration.
Note that I am not asking about dissolved oxygen just dissolved air in general. :)