Under the tank reptile heaters, wil they work for fish?

I posted this on on just freshwater, but I think it needed to go in
this group.

I had a gecko for 2 years who recently died, so I decided to get into
fish instead of reptiles, but I wanted to use what I had to stay
economical. I have a 10 gal tank, two reptile hides that I'll use for
fish hides, thermomiters, and an undertank reptile heat pad. It is
simply a pad that was stuck to the outside, bottom of the tank that
provides heat to the hot side of the tank (it only covers 1/3 of the
tank). It is 90 F on the surface of the thin mat of carpet on top the
glass area where it is underneath the glass. Once I get a UGF, water,
and gravel, it won't get that hot on the surface of hte gravel.

I was wondering if anyone had used this as a heater for a fish tank
before. Let me know. Some one earlier was worried about it cracking
the glass, but this heater only goes to 95 F and has been on the
underneath side of the tank for two years now and hasn't shown any
signs of cracking. THanks,

Ben