Substrate heater installation?
(A response on this NG told me it should be 50/50
Fluorite/gravel, which I guess I'll stick too.)
100% Fluorite is even better, but of course more expensive.
I have a 20w Tunze substrate heater.
I don't know about that particular one but I have heard a lot of people say
their substrate heaters didn't last very long. Mine lasted only a few weeks.
I suspect substrate heaters are of no real benefit to a planted aquarium
where the whole bottom is covered with plant routes anyway.