In article o2Rsg.5378$pB.2554@trnddc06,
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?

The original Dupla book which shows the cable installation in several
places doesn't mention silver sand at all and doesn't mention anything
in particular with gravel other than don't use fine sand which packs
too tightly.

Don't sweat it.


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