So, by my calculations, it took 9 - 10 weeks for the tubs to completely cycle at 38F-40F. Assuming that, on average, a typical pond will cycle in 4 - 6 weeks at around 70F. This means that at 38F-40F the Nitrifying bacteria and Archaea are functioning at, at least, around 40% of the conversion rate of 70F. This is considerably higher than I would have expected, but the facts have been presented! A pond does not shut down biologically when water temperature is as low as 38F/3C.