GGGRRRR..... Torches!

[BT05]

If you blast an LPS with too much flow, it will not expand properly and the tissue will recede exposing the skeleton eventually killing the coral. Especially working with 1 head frags, they need to be specially cared for until they are stronger. Then you can move it around.

Since you have been losing these, that should give you a hint about what to do. Stop putting them in the same location, lower the flow and acclimate it to your lighting. ie. try something different next time because what you're currently doing isn't working for this coral.

This is of course assuming that your tank is indeed healthy, no coral predators and the frag is also healthy to begin with. If you absolutely have to buy 1 head frags get ones that are about to split.