Pistol Shrimp - What is it?

[hfp75]

Here is a pic of my tank....

The emerald and pistol are not visible.... water has been stable, Ph drops down sometimes to 7.8'ish and I need a buffer to keep it up. Usually once a week I top up, change out water 10% and correct the Ph. Nothing otherwise as far as I can tell is a problem. I feed 1/2 a cube of brine shrimp a day & sometimes toss in 4-5 1mm sinking pelets (New Life Spectrum-Community Fish formula).



http://i101.photobucket.com/albums/m...5/IMG_0432.jpg