Each enclosure you have should have it's own thermostat. You definitely need get a second thermostat for your second enclosure.

I'd recommend hopping on Amazon and seeing if you can get one over-nighted to you, or if you have a local store that sells one that could be an option. Lastly if you can't get one quickly, you could run to a home improvement store and get an inline dimmer switch that the heater will plug into and turn it down to the proper temp with that, checked with a thermometer. But I only recommend that as a temporary last ditch fix until you can get another thermostat.

That's why I ended up switching to racks as I can house several BP's with one thermostat to control the whole rack. And if you build one yourself they are a ton cheaper and easier to maintain than tanks.