Glass tanks are not an ideal option for snakes or lizards. There are several problems that can occur.
The only access to a fish tank is through the top. Snakes and lizards tend to be very wary of things approaching from above (think birds of prey). Also the top is the only ventilation that is available
Glass can have very sharp edges so the glass supports at the top must be smoothed to prevent injury to the lizard and to you.
It's difficult to get a lid fitting well enough to make a fish tank escape proof especially for small lizards and snakes.
Heating is difficult, especially setting up a heat gradient. Using heat mats can crack the base, using bulbs to set up a heat gradient along the tank could be even worse. I'm no BD expert but I think they do well with quite a wide temperature gradient.
Glass is inherently brittle. Now a large marine tank may be fairly strong, but in general any glass container will shatter if it's hit wrong
If you do use the tank be aware of these issues and take steps to try to eliminate the associated risk.
It may be better to sell the tank and use the money towards a more conventional vivarium.