Crop Choice and Water Temperature

The summer and autumn seasons of my greenhouse aquaponics were a limited success.  I grew edible crops and found ways to combat excessive heat gain in the greenhouse with materials I had on hand.  Winter has presented a more difficult challenge.
My tomato plants were killed by the low temperatures of early December, however the herbs I planted in the other half of my bins have survived the cold and remain green.  The attempt to heat the greenhouse with a chimenea turned out to be destructive of the insulation on the ceiling, but the insulation which has deformed and withered probably kept the polycarbonate roof from melting.  I plan to do more work on the use of other methods such as a rocket mass heater, but at this time I will continue to use a propane heater to moderate the air temperature.
We have now focused on keeping the water system stable and preventing freezing.  We have a titanium fish tank heater on order and we have wrapped the pipes in the system with heat tape and added tube insulation.  Freezing in the pipes creates imbalance in the dynamic flow of the bell siphon system.  It also threatens structural damage to the tank and pipes  if the water freezes hard and expands.
Herbs and green vegetables such as spinach, mint, beet greens and cabbage resist cold air temperatures and continue to produce in the winter.
I can start crops like strawberries and tomatoes earlier in the greenhouse and keep them longer as the weather cools, but it is evident that I should switch them out for more hardy crops before sustained sets in.