Hey Matt,
I don't think you should be too concerned, they hid a lot when I had them. However, I would consider adding some fish that might bring them out a bit. Cyps or paracyps could help. I had those 6 cyps in my 150 gallon and they helped. I put shells in with a group of black calvus years ago and that they were gone. Nope, they were guarding a batch of fry.