I didn't look at the video all the way through, but that's a flat-bottom tank. In other words it doesn't have the standard plastic trim around the bottom. Whatever brand of foam gets used, the reason for it is to compensate for any irregularities coming from the flat surface it's set on. Looks like a rimless tank set on an untempered bottom pane in he vid. They have vastly different stress dynamics from a stock, rimmed tank with a tempered bottom panel.
Is your 125G a stock 125G with plastic trim?
What's the nature of the "irregularities" of your "support"?