Heat exchanger

The heat exchanger transfers heat from the circulation container to the cooling container, cooling the coolant that flows through the circulation loop. The heat exchanger is placed in the circulation container, but the coolant flowing through it comes from the cooling container

Each container has a pump that creates flow and stirs the water. This agitation makes heat transfer much more effective so you don't need a very big or long heat exchanger.

A recommended option is 30 cm or 12 inches of copper tube with a diameter that will connect well to your existing hoses. Bend the tube into a shape that fits your container.

Copper is more expensive than aluminum but it has better thermal conductivity and is compatible with Benzalkonium chloride whereas aluminum is not.

Another reason to avoid aluminum is galvanic corrosion. Aluminum is incompatible with stainless steel, which most pump shafts are made of.

If you prefer, you can use a copper block designed for heat transfer. It is more expensive, and you may need adapters to connect it to the hoses typically used in this system.