Well, I don't think that is the cause for the fish's issue and what may be eventual death. I am also concerned that these guys are open water swimmers, needing a minimum of a 6ft long tank to have enough room to swim back and forth in...but this is also not the cause of the issue at hand.
Why are you putting stress guard in the tank? If the zero'd parameters were true there wouldn't be a need for it. Generally, when it comes to saltwater, you don't want to add anything outside of water and your salt mix. Things can get out of hand quickly when adding any type of chemical or liquid whatever to achieve a goal that can be ironed out with nothing but patience and time...and a solid mix of ro
water and feeding minimally.