As long as your heat mat is regulated it's not going to crack the glass. Heat spikes can do that, but temps need to get real high for that to happen. Think of it this way: our bodies are over 98 degrees. Does glass crack if you hold it in your hands for a while? No. So a regulated heat mat won't crack it either.
You should be checking the actual glass surface temps with a temp gun. Then use those readings to adjust your tstat. Move it up a little at a time, check it again and keep going til your reading are 89-90. There will be variance from tank to tank, heat mat to heat mat, etc...so it's a game of trial and error. My tstats are anywhere from 92-96 to get 88-90 hot spots.
Reply With Quote