Is a heater safe resting on the substrate?

Question

ok i am setting up a tank to breed my danios

i have marbles on the bottom and an inch of water above the marbles (i was told by a very experienced fish breeder to do this)

the problem is the only way i can fit a heater in is if it rest on the marbles

is this ok or will the marbles get to hot for the fish eggs (danios)

it is a thermostat heater i think so it turns of when its to hot

whats the ideal temperature for danios, eggs and the fry

Answer 1

How are you creating water movement with such a low volume of water?  Fish don't like stagnant water.  No, you should never rest the heater on anything.  It will get a hot spot and crack, then it could electrify your fish or you. Get one that comes with suction cups.  Make sure the wattage is proper for your size of tank.  Too small and it will stay on all the time an prematurely age and die on you.  If you do have water movement, clear an area, block the marbles and stick the heater to the wall of the tank horizontally.  For the rest of your question you would need to consult your breeder friend(he should have told you this already if he's really that experienced)or a book on breeding fish.

Answer 2

Probably around 80 degrees would be good and it's likely that putting a heater on the gravel is unsafe for you and your fish.