I brought a Cornelius beer chiller on Ebay for £50, I've no idea which model it is although the seller advised that it was purchased to chill 2 kegs of homebrew at a time. The thermostat goes up to a maximum chill of 7. It has 2 lines in and out.
With no chilling at all the temperature in the tank under the lights can rise as high as 32C!
The chiller took 3 days to take the temperature down to 16C and now sits on a setting of 2 to maintain this temperature. The air temperature has been around 20C and it appears that the chiller stat will need careful monitoring to keep the tank at 16C as the air temp changes with the seasons. However, 50 gallons of water takes a while to heat up or cool down so monitoring does not need to be constant.
The chiller itself generates a lot of heat, I propose to relocate the chiller to the utility room adjacent to my office where I keep the tank.
Plumbing in the chiller
The chiller came with 8mm stainless steel inlets and outlets, this is an unusual size to get fittings for so I had to find a way to adapt. B&Q sell 8mm clear polythene hose for about 50p/metre, by softening the end in boiling water its possible to force the hose over the steel then a clamp can be used to hold it securely although it probably will not come off anyway. The 2 outlets simply have a length of this hose extending directly into the tank. At the inlet end its rather more complicated, the pump I used has a 20mm nozzle, to this I attached a short length of 20mm hose, once again I softened the hose in boiling water to force it over the nozzle, outside the tank I then inserted a short length of 15mm John Guest Speedfit pipe with the appropiate plastic insert to stiffen it and used a hoseclamp to tighten. Then I used a 15mm tee with 10mm reducers to connect to the 2 8mm plastic inlet hoses from the chiller. Once again I softened the 8mm hose and forced in a 10mm speedfit insert to stiffen the tube and this formed a tight seal when pushed into the 10mm reducer.
Its important to use only plastic pipe and fittings, ensure the inserts are plastic too. Metals will quickly corrode and poison the inhabitants - anemones are particularly susceptible to metallic poisoning.