It was many years ago and actually the first water I had. At a point where I knew very little about what I was doing with waters or any monitors. The heater was in a plastic pool. It was a visi-therm 150 watt heater which at that time was rather expensive. I actually got the idea of using the heater from some dimwitt who supposedly worked at the national zoo and claimed they never had problems using them with reptiles.
Many years and much more experience later. With out proper safeguards that are WELL thought out monitors water and electrical equipment can be a bad and dangerous mix.