That is advice. Adding this clam with only the advice of the person you bought it from is a big no no. The LFS
is a usefull device but go in prepared on the purchase. This is easy. Before you even fill the tank with water you should have a plan from water source to most if not all your stock needed and or wanted knowing there care needs upfront. Clams are filter feeders and help control nitrate. With low to no other stock then the amount of food you need to add means tons of waste that collects causeing poor water quality that clams dont like.
This is a fairly new hobby and theres lots still unkown. But a basic setup is known to work well.
Adding a clam so soon is like tieing your shoes before you put them on.
I am only trying to help.