Here's a thought.
The main reason you are having heat issues is that the volume of water is relatively low when compared to the intensity of the light. If you consider the same bulb over a much larger system (say 100 gallons), it is unlikely that you would be having the same problem.
The problem with metal halids is that they are inefficient. Some of the electrical power is converted to light but the the left over energy is converted into heat. This heat is transfered into your tank.
I'm not sure the technical term, but I think it's BTUs. It takes x number of BTUs to heat 35 gallons of water by 1 degree above ambient room temperature. It takes a much bigger X to heat 100 gallons of water by 1 degree above ambient room temperature (within the same period of time).
So, instead of cooling the water, you could also increase the water volume. Instead of a closed loop to a bar fridge (interesting idea
) you could run a closed loop to a sealed 65 gallon barrel. This would effectively increase your water volume to 100 gallons and would solve a number of your problems. You would likely solve your heat transfer problem, but would also increase your stocking capacity and overall system stability.
The best part - much less power consumption than a chiller.
I only suggest this as it appears that you already have the plumbing in place. It should be just as easy as plumbing in a chiller, but much cheaper and with additional benifits.
Might be crazy, but I thought it was worth the suggestion.
Take care
- Brad