When discussing substrate heating, people always use the same logical sounding premise that aquatic plants grow better with “warm feet”. Plants have indeed been shown to grow better with a substrate heater, but not because of warm roots. The reason is that the roots are supplied with nutrients more effectively. In their natural habitats, plants never have “warm feet”, except in extremely shallow water, because the bottom is ALWAYS colder than the water.
It is far more important for the heating cable of the substrate heater to produce water circulation in the substrate (warm water rises, cold water flows through) so that the minerals and nutrients constantly flow around the plants’ roots. The resulting plant growth is enormous and the amount of nutrients which might cause algae trouble otherwise is reduced because they are consumed more rapidly by the plants' roots.
JBL is launching a new generation of substrate heaters (incl. slotted suction holders for mounting) under the name of JBL ProTemp b, available in four different sizes: