I killed my brown powder tang

I would also like to know your ammonia, nitrate, and nitrites. Also, is this Thera-A SF mix a veggie/algae mix? The meat mixes are not what you should feed a tang, as they are mostly herbivores. Sure they will take mysis and what-not, but they need veggies to survive. Also supplementing broccoli which you can tie-down on a rock for grazing is a good idea.
I honestly don't think the change from 1.024 to 1.019 in SG and a drop of .3 in PH would kill the tang that quick. Tang's are tough, hardy fish. My tang even lived through an anemone death, which did a heck of a lot more than to the water params than what you describe.
My guess is that there are other water params that are way off as well, and have been for some time, or malnutrition.

And topping off is a part of tank maintenance that needs to be performed daily. I couldn't imagine what would happen if I let up on that here in 0% humidity land. I have to add about a half a gallon a day, and that's just on my 40.

 

healthy fish just dont die overnight. ph is a log. scale. you do know that? they stress easily (due to IMO rapid salinity changes/temp/ph) anysigns of ick?

 

My post was not negative at all, sorry you took it that way, i would not dare come in here, ask a question, and reply in a negative tone.
My specs are as follow.
FOWLR
Weak lights
Temp 78*
Ammo 0
Nitrate 0
Nitrite 0
Ph 8.0
salt 1.019
I put a clip of nori once a day, the tang and fox face love it.
the SF Mix and Thera-A SF mix contains veggies.

 

Was the fish acting weird before? I lost a powder brown tang that was acting fine the day before. It can just happen if the fish was new or stressed.

 

No he was not new, i think he was nutz, he would fight his own reflection all day, he would do some other crazy stuff, thats why i liked him so much.
His name was brownie.

 

Do you have a ground probe in your tank. If not get one.

 

No probe, this weekend i think i am going to setup a automatic top off system, and add a probe, When i do top off's i have been doing FW, but if my water is evaporating so much, should i add some salt? and maybe put the glass tops?
Thanks for all the help so far....

 

That's not really what I would consider odd behavior. As far as the fish was concerned, it was defending its territory against another powder brown

 

Well definitly add the probe. For top off's you should only top off fresh water. Salt will not evaporate no matter how much water evaporates. I'd try and slowly raise your salinity back up as well. 1.024 to 1.026 is the norm.

 

When I worked at the LFS, we kept our fish tanks at 1.018sg and the store is still known for having the BEST fish. Ive let my 75g evap 10gs before and topped off all at once with no ill effects whatsoever. The ocean, the salinity can change at the drop of a hat. Every hurricane/typhoon/big wave, the salinity changes. Dumping thousands of gallons freshwater from storms on shallow reefs definetly changes the salinity on them with no ill effects.