Hello I have never heard of the dorsal fin drooping on a Clown loach, ill have a look into that and get back to you on that.
you added 3 new ones to your tank did you quarantine them before you added them to your main tank?
Need some details to help you
Size of tank?
stock in tank?
Filtration?
Water stats i.e PH, Ammonia, Nitrite and Nitrate?
Have you lost any fish lately?
How often do you clean your water, amount?
size of the clowns
The colour loss is commonly known if there is no other underlying problem, as greying out and it is common in clown loach community's
Have you done any research on clown loaches before purchasing any of them ?
Get back to us with all this information and we may be able to help you
regards onebto