Hi all, just want some advice before I buy them, can I mix blind cave tetras with a mature red tail shark? Thanks in advance. Don't want to get them and then stress them with the shark

This is a hard question to answer as a lot depends on the shark. Have you added other fish to the tank recently? These fish often tolerate fish they have grown up with but attack any new species added as they consider the tank their own territory.

Red tailed sharks can get pretty nasty. You can get pretty friendly tigers but I have no desire to pat any of them.