Most pumps (yours included) are cooled by the water that flows through them. So if you resevoir runs dry, you will end up with an uncooled pump.
The uncooled pump will have a potential to either burn itself out or burn other things. both of which as been either seen or experienced (not by me though).
The other down side to that pump is the noise factor. It is almost as loud as one of those electric etching pens.
Other things to consider is that with that clear tubing, you will likely get alot of algae build up in that hose which you will need to clean.
The system while workable is cheap. And cheap for a reason. If you can I would recommend returning what you got and spending the extra scratch for something I know you will not recommend. Mist King, Herp Mist, Promist, or Rain maker are the more common brands of systems on this site.
I personally have decided to go with
Herp Mist. I spent a pretty penny but my whole reason for spending the money is, safety,fill and forget, and regular moisture for the chams. Thats just my opinion.
Hope that helps..
OPI