29g JBJ HQI

I have a yellow sailfin blenny that is looking terrible today. I though maybe he looked poor yesterday but I was gone for most of the day and couldn't observe him. Today he's bad. Not moving much, his bright yellow is turning black/grey, and his respiration is very fast. I also noticed he does not have his normally fat round belly so he hasn't been eating.

Beemer and my tailspot blenny are fine and acting normally, swimming about, searching for stuff to eat.

I had my tank water checked about 3 days ago and all was good except my calc and alk were low (on going problem). I did a 5g water change about 2 days ago. I always run carbon and filter floss, cleaning those daily.

Could a PH swing cause this? I'm having real issues with my PH. I have a hard time keeping it around 8 and overnight it will drop to 7.8. I use 2 part dosing and just started adding magnesium (maybe magnesium is to blame?).

Very worried....must save blenny



PS - I indirectly blame this on karma and my chat with addboy a couple days ago where I assured him that I've never had any problems with my blennies and they seem to be very hardy.