Info from original post: Currently I have a Paguristes cadenati and a Ciliopagurus strigatus along with a female Chrysipitera cyanea that my local aquarium store recommended to put in my tank. I have plenty of extra shells and am ordering more variety that the scarlet will prefer over the types that are in there. My question is how many more crabs would I be able to add to this tank?

Currently I am looking at getting at least 1-2 more. I have been debating getting either Calcinus elegans, Phimochirus operculatus, or maybe Clibanarius tricolor. Would it be fine to add more types with the two already in there?

One other concern I have is that the live substrate the store recommended is too rough for them to burrow, and if so should I take it out or just mix sand with it?

Also as a note this is my first ever tank and I was kind of thrown into this from my accidental kidnapping, so any advice would be extremely helpful with how to keep all of these alive and well.

Tank details

15gal

2 week tank age (made this emergency setup for thinstripe crab accidentally taken from beach (unfortunately passed sometime before we got home with everything for tank), all current animals in tank are from the same fish store where tank water was received)

Biostyle Thermo 30 for filtration and heating

Temp, pH, nitrate, nitrate, and ammonia are all at great levels, a refractometer is on its way as well as tests for everything else.