I think mine was from Maplin. It was run straight from the nutrient solution at every flood cycle - so no, not in distilled water - but I replaced the transducer about once a month, so that will be linked to the information you've got. It probably isn't needed strictly speaking if the humidity is correct, but it gave the plants a more pleasing look. The Java fern for example looked quite poor when dry, but epic when moist.....did it need to be moist? - Probably not....
