[Oldreeferman]

I've got a couple multi colored Ricordeas and i have noticed they need a mature tank to be comfortable & grow. They tend to be good hardy canarys to show how stable a DT is like GSP is also. Pretty but sensitive new tank choices.
Beyond mature params they also do much better if fed at least once a week otherwise yes they don't grow much if at all, or will actually shrink over time depending on nutrients in the water.
I feed both of mine once a week brine shrimp and switch to a couple .05 Coral Frenzy pellets every other week to give them a feeding variety and the feedings really make them grow fast.
I use a spot bulb feeder after all fish have had their fill 1st and turn off all water movement for 10 min or so until all food is consumed. Tedious but fun!
They like being on the substrate bottom period.... so if you can move them do it if they are not on the bottom tho they can tolerate higher lighting then normal run of the mill mushrooms can,... if acclimated slowly, always start them at the bottom tho and move to a shady spot if the lighting is too bright.
If they still are shrinking & don't want to eat or grow after locating at bottom still then its too early to have them as they are sensitive mushrooms to new not fully established DTs.
Not a really good beginner mushroom, better down the rd. when the tank can handle LPS corals etc not just softys, i had same issues when my DT was too new, luckily they survived the 1st yr. shrinking then eventually eating & growing.