Hi Kyle - I just sent you a PM, but here's what I had in it.........
Hello! Since I set up my 130 over 4 years ago, I've never been away for even a day, so I'm not the best at preparing for 3 weeks away. You might want to put in a post in the RSM Club asking for advice.
My own opinion - since you have no fish, the biggest issue to deal with will be getting someone (friend or neighbor) trained to manually top off the tank with fresh water (preferably RO/DI water) - to make up for evaporation. Other than that I'd probably remove any sponge or filter pad that might plug up and cut flow through the back.
An ATO (auto top off) might be good, but it may be difficult to plan on how much water you'll need in an ATO reservoir to last 3 weeks.
I hope that helps.
Terry