i wouldnt recommend coconut fiber
they turn dark when they r unhappy or r trying to blend in
u should either use rock material as land or softer soil such as plantation soil or moss of any type as long as it's meant for reptiles/amphibs
they dont need uvb either and idk if it's a good idea to have it in their bulbs
focus the lamp over one area of the tank and dont let it get higher than 74 degrees