That comment probably needs qualification. I'm in California, and even here
an
unheated tank runs aroung 66-68F during the winter, possibly colder at night
if
its a small tank. An awful lot of fish are going to have trouble below 70F.


Hehe, your comment needs qualification too
Depends on where in CA you live, I lived in Southern CA for a couple
of years. Never used a heater, had Rummy noses, Cardinals etc. Tanks
stayed about 75F minimum.
Never heated the place. In the Bay area I heated some tanksm, like the
Discus tanks but nothing else. Fish where fine. 72F or so is okay,
below that., heater time for many fish. If you catch your own locally,
then colder is often better.

I collect my fish from the wild these days, no need to change what
they are use to.

But the high temps + low O2 levels can complicate things, 2ppm of O2
is a fair amount of difference and within these temp ranges this can
occur or more.
My lights on some of my tanks cook things pretty good.

Tank size also plays a big role here also. A 100 gallon tank does not
move as fast as a 10 gallon temp wise.


During the summer, of course, the heaters seldom turn on.


Florida here. No heaters either. The tanks never get below 75F.

Scott