Gettinggnashty

Greetings, Unfortunately my first post in this forum has to be sad. I have been losing shrimp at a very slow pace. 1 every month for the last 3 months at this point. Originally, I thought it was simply due to old age, but I just found a shrimp that may be infected tonight, and was wondering if that may have been the cause of the other deaths? Poor fella is now in quarantine. The spot sits just under the carapace of the shrimp on his right side, you can almost see a "bump" where it is located, the carapace bows out ever so slightly. It is whitish, with a smaller circle inside that is significantly more white. I only have one tank, 17g display with lots of plant life and everything has been pretty good for the last 9-10 months, not a lot of death that I noticed, unless the snails got to them first... Water params have been very stable, have not seen any swings: ph: 7-7.2 gh: 8 kh: 8 TDS: 250-300 temp: 70-73 I dose ferts for the plants at half dose (1ml) flourish excel. water changes once a week 20-30% the first picture in the link is the first dead shrimp I ever found, thought it was old age/bad molt? maybe I was wrong? Second/third picture are of the second shrimp, almost identical in every way to the first one, even the same spot of death in the tank. rest of them are the shrimp in question http://imgur.com/a/32JGi Thank you for your time!