Mixing valve is a great idea!! What about the line run? If it's say...5' or so and dripping 1-3gph do you think that by the time it reaches the tank it will have cooled to the air temps? The tank itself is 540 gallons, I have 2 55 gallon drums and a 100 stock tank as a filter, the stock tank is holding about 75 gallons of water and I'm moving about 3800-4k gph. I have a single 800w heater in the stock tank now. Am I moving too much water to try and heat the stock tank which in turn heats the tank? Should I just put the heater in tank? I'm at 74 degrees now, I don't have lids yet but maybe once I get lids the temp will bump up or will I need more wattage?