Ive never met anything i couldnt get off with a little denatured alcohol and a razor blade.,., but like said before Id work with something softer before you go chemical style.,., unless your not planning on using the tank for a little and you can take the time to thoroughly clean off any chemical residue that may be left over.,., itd be a damn shame to do all the work to clean your glass only to have your fish floatin at the top cause something harsh got in your water