So my first temp reading was at half 2 this afternoon after topping my tank up from its 1000ltr ibc tank un insulated in the garden and that was 5.8 on my tds temp stick. In 1, 45hrs it is reading 10.5 so an increase of 5degrees in just under 2hrs. Now will that just increase at that basis or will it quicken up as now its heating 10.5 and not 5.8, i have no idea on the science part. But i probably will take a reading a couple of hrs later out of curiosity