Corrosion Products" test kit. It consists of an electrode and a multi meter with really long leads. You drop the electrode into the water and test all the underwater parts with the other lead. You connect the leads to the common and volt/ohm red and black banana plugs on the meter and select the 2 volt DC range. You read the volts and record what you find. You could do the same thing and make your own electrode by using something like an old silver tea cup or candle holder. Dan was kind enough to give me his test kit because he's a nice guy.