Any way to label frags growing in a tank? Last semester, students set up various little investigations and always had difficulty tracking growth because they lost track of what was what and it seemed things always got moved, so diagrams of placement did not work either. We had enough trouble with colored strings outside of the tank degrading or falling in that I am leery of using them in-tank. Zip ties? I guess those would be okay on frag plugs as long as they did not come off. No permanent ink, right?