cause of death

[rng_pw]

I have no idea what is going on in my tank right now. Everything has been doing great for the last year and then all of a sudden I have lost 3 fish in the period of 2 weeks. A hawaiin flame wrasse, female blue jaw trigger and today I found my sohal dead. All of my parameters are right where they should be
ph 8.2
nitrate 0
nitrite 0
ammonia

calcium 375 (lower than normal but Im trying to tune in my calcium reactor)
Alk 7 (normally 10, but has been lower without any issues)

Tank is a 450 gallon reef
Any ideas as to what might be going on. I seen the sohal yesterday and he looked fine. My achilles used to pick on him but it has been weeks since its happened. Thanks in advance

 

[Demonic]

Feeding any new foods lately? Dosing anything new? Are you doing anything differently?

 

[AlexStinson]

trying to dial in calc reactor? maybe a little too much CO2 got in the tank?

 

[rng_pw]

Feeding any new foods lately? Dosing anything new? Are you doing anything differently?

Well I started doing water changes. I never did water changes until about a month ago and I do about 30-40 gallons a week, but I cant imagine that being a bad thing you know.

 

[rng_pw]

trying to dial in calc reactor? maybe a little too much CO2 got in the tank?

I was kinda wondering that my self. I have it set on a ph controller and the drip line is about 8-10 inches off of the water. If this is the case how would I know and what can i do to remedy the situation?