by Frank Gapinski, from Ecofilms posted on the permaculture.org.au website.
“Here’s a great tip given by a member of the Aquaponics Made Easy Forum on a cheap easy-to-build hot water system using compost.
The original question posted to the forum was “how to heat a fish tank over winter without any extra energy costs?” A hard thing to do. Thermal Mass heating was one answer but a crafty member posted a very interesting solution and swears that it works a treat. We’ve illustrated his simple design. It’s so simple you will think “Ah-ha! Why didn’t I think of that?””