Brewed a Kolsch today and had a tough time getting my wort temp down, even with a prechiller (an extra immersion chiller in an ice chest) in my chain. This is the warmest I think I have seen our tap water, and it's not even summer yet. I know some folks use an aquarium pump to recirculate ice water through their immersion chillers. Is there a pump that someone has used for a long time that's very reliable? Also, please tell me about your method. TIA!