Hermits dying off

Well, there are four things I think it could possible be:
1. Tank was not established enough for the bioload too quickly
2. Stray voltage harming inverts due to lack of grounding probe
3. Nitrites are present in your water source, so you are just constantly adding them with top offs and what-nots
4. Copper was used in tank before hand and is now leaching into the system.

The first thing I would do is test your water source. If that checks out, order a copper test kit and a grounding probe (should have a grounding probe anyways).
If all that checks out, then you know it was #1.

 

I am inclined to believe that the tank is in the middle of cycling.

The last two of the 3 hermits died and my nitrite reading today was .2. I changed 2 gallons of water out to ease the stress on the remaining livestock and will recheck the nitrites tomorrow.