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In my experience with regular flex PVC (haven't used the ultra flex yet) it seems to slide into fittings much easier than standard PVC when gluing. It can also seem to "pull" back out as the glue dries if not held in place. Did you use standard PVC primer and cement?
Looks like growth to me. If you can snap a picture when the rest of the lights are on. Many SPS have a different color in the new growth such as tips of SPS.
Good advice above. Many chalices are very sensitive to alk swings or changes so I bet that was the case. Hopefully with the dip and things settling in it will recover for you