Need help with heat!!! ugh

Okay so I have a ZooMed 10-20gal heat pad and a repti temp 500r therma-stat (yes I know). The problem is when the therma stat is in the heat pad looses heat, with just the heat pad in the warm side gets to 92 but cant get the cool side to get pass 75 don't know what I could do??
Please if anyone have any ideas i'd love to hear them....
also I'm using a 15 quart tub

Your problem is related to the tub. Tubs do not hold any heat at all, the pad will maintain your hot side but disapates faster than it can warm the cool side. There are a few things you can try, insulate the tub to hold some of the heat. heat the room to 80ºF or a second T-stat and pad (I would really NOT recommend a zoo med for a two UTH set up as they will allow the pad to get quite hot before shutting down.) try insulating the tub first. 75 is a bit low but if you can get it into the high 70s You'll be fine.

Nothing wrong with 75 for the cool side...

Hey thanks a lot guys that makes me feel better, its getting up to 77-78
Thanks a ton I can sleep easy

77-8 if perfectly fine I don't like seeing 75 during the evening as it often drops a bit over night.