Hello; I will assume that you are refering to the plastic trim that goes around the perimeter of the bottom. While i have not foxed a tank as large as a 230 gallon, I have fixed smaller plastic rims. The most recent was when the bottom trim came lose. It was fairly simple to put it back with a good line of silicone.
I would go about your issue in a different way. First try to determine if the glass was affected by whatever cracked the trim. If the glass seems OK, then I would likely patch the crack with a two part epoxy. There are different types of epoxy. Some cure very hard and others are more flexable when cured. I would go with a more flexable type, read ther label. If you have not used epoxy, it might be good to practice with it a bit.
You might also do a search of this forum. This issue has been posted before.
good luck