temperature probe for DIY hillstream chiller?

[cloudhands]

Cooling the hillstream river tank:

Right now I have a little woodstove fan on a lamp timer blowing down on the water surface, set to blow about half the time. I fiddle with the timing a bit depending on ambient temperature, but it does keep the hillstream river tank around the mid-70s with some fiddling and variation. This is to offset two 60w powerheads and bright lighting, which tends to heat the tank well above ambient air temp. Sometimes the system fails for various reasons, and we do get some swings, mostly on the high end.

The upsides of this are that it's cheap, and the fan on the water surface is probably great for oxygenation.

The downsides: It evaporates the tank, and also contributes to the humidity in the house. I'm worrying we're actually looking at moisture problems in the house with all these tanks.
Also, it's not designed to blow down (it's meant to blow the hot air near/above a woodstove around the room). The bearing is starting to complain a bit.
And also as I adjust for changing ambient conditions, I risk messing up and getting temperature swings.

I was thinking if I could get a temperature probe swtich, attached to a small submersible pump or powerhead, and attach that to tubing. In the winter the tubing could run along a long, cool shelf under a lot of windows (in Vermont). This would be cool for three seasons.

In the summer (or all year) the tube could go through the floor into an unheated (but somewhat insulated) crawlspace. It doesn't freeze down there anymore, and it certainly never gets warm in the summer.

Really the only thing stopping me right now is finding a suitable probe-switch. I've just spent some time I should have spent on other things with google and on fish-store sites, and I came up short.

Any ideas?

[mattyd]

my suggestion:

mini temperature thermostat.

Check Ebay. It is a PID type control device.

You would program it to power on a pump when the temperature gets too far one way or the other. Ie, in a normal usage you'd connect it to a heater for when the water gets too cool (it has an inbuilt relay that the heater would get plugged into). When the water is in the "okay" band, it would turn off the heater. When water gets too warm it would activate the relay for the cooling system (ie, a fan or a chiller).

In your case, since you are having issues keeping it cool, I would run the piping into a cool area of your house and have both ends of the piping in your tank. Have a pump that is connected to one end of the piping, and it is powered on by the cooling relay of the thermostat.

When the tank is too warm, the thermostat will power on the pump. Water will be pumped under the house, cooling it, and exit into the tank. Just make sure that you have each end of the pipe covered with mesh to prevent fish getting into it, and probably have it done to come on once or twice every day to keep the water fresh.

In winter, I would just recommend using a tank heater to keep it warm.