Here is how it's done. See the attached screenshot. Its relatively easy to find if you know what to look for, but like I said, he hasn't found it, and I don't think he will as he just likes to make new tanks and such. But if / when he does, I'll deal with that later.
I hope this is something that can be done. I love this aquarium. My son has loved fish since he was 2 days old (because of this product) when I was holding him in my arms and his eyes were as big as saucers trying to get a look at the fish.
http://picasaweb.google.com/nytiger7...36432140026402
If you can't see the image, let me know and I'll find another way to show you.