I know you said your alk is 9, but a few things to consider:
1. Have you double checked with a second alk kit, or a known alkalinity number (salifert now includes reference samples)
2. Are you running as ULN, or running GFO? higher alk with very low NO3 and PO4 often leads to tip burns.
As far as the tips, you can break them off, but they'll probably be grown over again when you solve your issue.