Ok. So from what I read, you did a water change and the fish died & the corals are unhappy.

You better find out what is the problem with the water (probably too much kH if that's what you added this time) before you compound the problem by doing another big water change and adding to the issue, instead of solving it.

With tapwater, are you using Prime or what to treat for chlorine? Maybe the city added chloramine in the water system.

+1 on the chlorimine, if it is then you might need some amquel to get rid of the ammonia.

What's ALK ?
I'M going to do water change 30% and I'm adding prime

HUH??? That's a new one. No offense to those who my work at a "pet store". But that is where I have heard the most bad information given out to people. Go to a store that specializes in SW. You should NEVER add anything to your tank that you do not test for. Get yourself some test kits and try to learn to do your own testing. And don't let the stores try to sel you the Hagen Master Test Kits which are for sale at most "pet stores". And to answer your question on what's Kh without gettin into too much long winded detail, it's Alk. By the way the quotations are for the chain stores. Once again try a SW specialized store.

Alkalinity or carbonate hardness (kh)
Should be about 7 to 9 dkh.
the kh additive is raising your alk (kh)

couldnt have said it better:)
how can you know what to add if you dont test for it.:)

mohammad, you don't live too far from J&L aquatics. Take a water sample ( about a half liter ) and ask them to test your water for PH and Alkalinity. They'll tell you what's wrong with your water .

IMO, and just from watching the video, something must be way off. Please get a test kit for the basics and maybe copper too. Test the tank so you know where you are at and continue with water changes but test the new salt water as well. Could be anything causing the problem and you will find it if you keep looking. Bad salt, bad fresh water, low oxygen, high nutrients, heavy metals, etc.

Best of luck to you.

i took my water to 2 pet store they telling me diff things about my water
im confused , i dont wanna name the stores here .
one of em told me the KH is good and the other one said the kh is high

J&L has new rules for testing water on the weekends
if you want ur water to be tested
you have to know what do u want to be test so they only test one thing