the worst i have had was a 6x2x2 bottom glass cracking from one corner to the other , lucky there was no fish in as it was still cycling ,the whole tank emptied into my front room while i was at work, the lfs where i bought it tried to say it was my stand ,and then came up with ,it might be because your using 1" poly under it i think that is too much, however after a bit of a battle and getting another lfs to check the tank admitted it was not built square, he replace the tank but refused to pay for any damage , luckily i had house contents insurance that payed up , they paid for a new stand ,sofa ,carpets wallpaper and fire surround , needless to say the wife was none too pleased , esp. when after 6 months i said i think i might get a bigger tank