The Max-E-Therm heater uses a specially made Cupra Nickel Exchanger.

• Easy to install. Just hook up to your gas line and plug it in.
• Digital readout of pond temp and the set temp.
• Energy efficient with an industry rating of 84% efficiency
• Water enters in the top 2" union fitting circulates through the cupra nickel exchanger
  and back to the pond via the bottom 2" union fitting.
• Available in 3 sizes

So, now the waters getting cold and your koi are starting to become a little lethargic with the cooler water and that's not a problem, or is it?

It normally goes something like this:
Water cools off, Koi stop eating, they live on their reserves through the winter, water warms up, immune system compromised due to lack of nourishment, pathogenic bacteria comes on as the water starts to warm, the bacteria is happy cuz' it just entered -

The Aeromonas Alley Zone

The result = everyone's favorite, Good ole Hole disease. But that's ok because you enjoy catching the koi, knocking it out and then injecting with Antibiotics just so you can save that much treasured Showa, that you saved for the last 6 months for, and that you were planning to enter in a couple months at the next show. However there are no categories for fish with giant healed bald spots.

Solution: Be smart, heat the koi, keep it feeding and strong. The immune system will be running at Max and can help defend itself against the ugly bacteria that robs us of the joy of keeping our beloved pets.