I agree with all the above you need a better thermostat, and two of them. The only time you can run 2 racks on one T-stat is if the racks are identical, and then I still would not recommend it long term.
This is not directed specifically at the OP, but the price and availability of theses things really should be factored in to the overall purchasing, even if it means not getting the next snake to ensure you have the proper gear and do not injure/kill the ones you have. When you have multiple racks going, you are beyond the "I am new to this and just did not know" phase IMO.