may be the stand is not tight at all the joints
i had a buddy with a 55g that had a problem with it doing as you described, we went and sunk a few more screws into the joints of the stand to help tighten it up. the problem went away
that certainly is something to think of, but I'm pretty certain theres tons of screws. There's enough and some more in there haha.
lets set this straight for some people since I edited my posts to make it sound less dramatic..
The water does not slosh as one would imaging "sloshing" I chose the wrong word.
From simply jumping down the water picks up a ripple, doing it a few times in succession can cause the ripple to increase exponentially but seems to be at a certain frequency only. Jumping really fast around the tank would do nothing but scare my fish. Slowly and the energy within the water builds and builds but never the point where I'm assuming damage would be caused.. It would take some stupid retarded person around the tank to worry me.
I over exadurated lol, wrong words.
I am just curious whether or not silicone joints can at least handle a bit of force from water moving back and forth within the tank. Dumping a couple gallons of water violently into the tank or causing some waves using your hands would cause something I would genuinely worry about tearing apart the seams
ps: there is a myth that those familiar with the show MythBusters put to the test. I'm not sure of all details of the myth, but it included many marching men going down a bridge. The bridge apparently started resonating with the stomping in succession of the men and energy built from a slight vibration not even noticible to building up to large swaying which resulted in the collapse.
it is this 'resonance' with which the water is 'occilating' that I'm talking about. It's interesting yet scary!