could be a bad valve. only thing i could think of.
whatever you do, constantly check the water levels when the power is off so you know it wont flood when you actually are away from home.
That is a great place to order fish and inverts online from. I would look someplace else for corals personally, just due to prices and options, and live rocks as well. It would be cheaper to get dry rock from places like marcorocks.com and then get just a few lbs of live rock locally.
When you order live rock online it ends up being mostly dead when it reaches your house, and you have to recure it which is a very stinky process. Plus paying for shipping is quite expensive.