How can I get spackle off one of my tanks? Any help would be good.

QTip and water. Little dab of water on the qtip and a bit of rubbing. Go slow carefully. You could also try to 'pop' off any larger chuncks with a sharpened toothpick.
I have used the QTip method and it's a bit slow but it definitely works. In some of the crevases I use the toothpick a little bit to chip small pieces off.

THanks for the help.