Ok, hmmmmm..... along the lines of what you been doing so far. Let me think here for a second, hmmmmmm........I take it that you call to ask the people that make the Zoopoxy if there was anything that made removing there product easier right
Maybe you had the right idea of sealing over the stuff just that you where using the wrong sealant. Maybe you should look into wax as a sealant or liquid acrylic. Either of these should seal whatevers under them, say to a depth of 0.5 ~ 1.0 inch above what your dealing with now. And then you could start all over again. Yeah I know you have all this crap below, so you build a recessed stand.
This tank will never be.
I will be selling the filters,pumps, etc. that were set up for 220.
Also, anyone willing to make me an offer on the 220 please PM me, I'm practically giving it away.