maybe those embroidery hoops with screen in between them. you should be able to find one the right size. they make square ones too. it would just sit on top of the tank and the weight would hold it down. use the plastic screen and plastic hoop.
Actually, now that I think of it, maybe I will go to Walmart or something and just get a vase or jar for this setup. Maybe it will come with a lid, that, and I looked online and turns out the Petsmart tank is about $5-$10 more.
True. And most importantly (in this case) they have those big Heritage Hill glass jars for about $10. So I think I'll use one of those and maybe drill a hole in the lid about an inch big for air and possibly growing semi-aquatic plants out of.