Pseudocorynactis popping up. good/bad?

so all of a sudden I have these small multi colored anemones popping up on a few pieces I of live rock. After a lot of research on line I've settled on Pseudocorynactis for the Id. These guys are pretty benevolent and kinda add a little low maintenance splash of color to my tank. But recently I've had two cardinal fish kick the bucket and I'm wondering if these new additions are to blame. The first cardinal just went missing. No surprise, I have a large cleanup crew including a chocolate chip star so any dead fish could be taken care of rather quickly. The second cardinal I kinda saw the final stages of his demise. He was barely swimming and appeared to be paralyzed. He stayed alive along time breathing but not moving. I think he may have been stung by the Pseudocorynactis. The other fish in my tack are rather fast and nimble swimmers but the cardinals are rather slow and kinda dumb ( sorry if this I offends anyone, They just seen a little on the slow side to me). Anyone have Abby experience with these nem/coral whatever you want to call them. There is mixed opinions on them as to keep or eliminate them. I like them and since I don't have three lighting for property reefing I considered this a nice little consolation.

 

I saw a small strawberry nem killing a giant potters angel in the LFS the other day I thought was silly. Stress from new acclimation plus some little stinging might be enough to put them over the edge.