i would hold up as long as the water was in the tube before it was set up. It works like a Utube on an overflow, jsut if the water stopps. The water levels become even and water doesnt come crashing down because there is no air to fill the sapce. and water doesnt realy expand like a gas does either.
And your right, my fish so woudl follow me around, esspecialy my clownfish always begging for food!