Like I had said in a previous thread man, the pH. Fish/inverts hate one thing more than another and that's pH fluctuation. You need to keep that **** steady. .2 is alot bigger for fluctuation for those little twerps than you think. Be happy with keeping two or three fish until you get a good steady pH going. These are my last two cents. I've been preaching the same thing since the first thread. If you don't detect metals, but your pH fluctuates and your livestock keeps on dying like houseflies, then it's YOUR PH.
Also, have you ever thought that it may be the fact that your tank isn't fully cycled??? You started this tank about 17 days ago and have gone through 3 damsels, a royal gramma, green clown goby, and atleast two shrimp. Wait it out before adding anything else. Let your pH settle. Let everything settle. Patience young grasshopper.
You post and post and post of problems and some of us have been identifying your pH as a potential problem but you keep buying and killing fish without keeping it stable. If your intention is to ask and just do what you do, then why ask?.