Mark Newcomb wrote:
Hi;
I have a 125 gallon for which I purchased a Dupla undergravel heater. I was
about to add flourite (my favorite substrate), when I looked at Peter
Hiscock's Aquarium Designs. On page 29 hes says that you "must" use silver
sand to cover the cables.

Does anyone knnow if I do need silver sand as a bottom layer?

Thanks

Heating cables do not do anything, you wasted your $$. You might feel
better spending more on your tank, but these do not help plant growth
in anyway.

I've used them for 10 years on 7 different tanks.

They do not do anything.
Tropica, one of the largest growers of aquatic plants also agrees.

So..........

Regards,
Tom Barr