well... I tried running pond water thru the 100 feet of clear tubing
from aquatic ecosystems. the water was definitely warmer at the
outflow around 1 degree difference with a slow flow. But I got an
incredible algae bloom. the algae was growing on the inside of the
hose, so it was working as a veggie filter. however, the algae also
would come off in clumps when stepped on. I disconnected the tubing,
turned on the UV and the water cleared in about a week.
pfffft.
I may need to slow the flow and attach the outflow directly to the UV.
In any case, it does act as solar heating. Ingrid