What's wrong with my clam?

[JeannieS]

My clam's foot has turned black. I inspected for any parasites and I don't see anything. It is still opening normally and I only saw the discoloration by chance when I accidentally knocked the clam over. Nitrate is 5, pH 8, dKH 8.3, phosphate .03, calcium 455, mag 1380, SG 1.026. I have been feeding it with puffs of phyto from a syringe upstream from its mouth. It's been in my tank a little over 2 months. Any advice would be appreciated.

 

[GHOSTLY]

So ive kept clams before long ago. If its opening and eating it should be fine. What are you feeding?

 

[JeannieS]

phytoplankton - a few puffs upstream from his mouth daily