for what it does, you really can not beat the aqua Jr, otherwise there is the DIY attempts at it and there is the controller that LM is suggesting. My fans cycle 24/7, but then again I have a +/- 2 degree temp variation.
Myself I looked into doing DIY what the aqua Jr does, and by the time I would have gotten all of the parts, I would have spent more, not including the time I would have spent.
below is the price from neptune, there may a used one around also.
Starting at $149.95 the AquaController Jr base unit
delivers the highest price performance ratio in the
industry and brings truly affordable aquarium monitoring
and control to tanks of all sizes. The AquaController
Jr has the same great programming configuration language
of our higher end controllers as well as the temperature
and pH monitoring and control, lighting and pump/powerhead
control. Read more
here.
Now bundled
with the DC8 at the amazing
price of $224.95!