Regarding Pinched Mantle:
I was given this tip by someone who's had clams for a very long time. He said that if you suspect a clam to have PM, first thing you should do is to determine if parameters are good, water flow, lighting, and once you've checked and crossed those off your list as not being applicable, add fresh carbon to your aquarium, wait one week, if the clam hasn't stopped showing PM, then you can proceed to a FW dip. His exact words were "too many people rush to PM when it can be something in the water that needs to be filtered out by carbon".
I have a maxima that was exhibiting the exact signs of PM, I asked my friend what I should do and he told me the above. I skipped the first three parts and added carbon immediately and also reduced my LED white channel to 80%. The clam is fine now.