Hammer coral question

[iceman86]

I've had various hammer corals over the last few years. In my tank the tentacles are always thin like this

https://www.google.ca/search?q=hamme...oW6WhNKpbYM%3A

I've seen them in stores looking full like this next pic and when I bring them home they become thin.

https://www.google.ca/search?q=hamme...HhjjKFbpAnM%3A

This is the second tank, have used t5 and led yet nothing changes. They are healthy and always multiplying. Nutients are always low and stable patameters. Any ideas?

TIA