well first off, how old is your bp? a 50 gallon tank is huge....very huge. especially if she fit in a 20. as for the lights, i dont think any of us will be able to tell you what to have on and what not to. your gonna have to play around with it to get the most heat. 70 is cold for a bp. and if you went up to a 50 you are going to have even more problems keeping the heat in that one