Tank is crashing :(

[MitchM]

Originally Posted by iceman86

Thing is, I haven't really changed the parameters too much. They went up slightly but that was over the course of weeks so it shouldn't have bothers them right? Only real drastic change was the t5 to led but that shouldn't kill every coral in the tank.

I'm still thinking it's the sand bed that's releasing hydrogen sulfide because of the smell. I decided to remove half of my sand bed last night and the water and smell was disgusting. I'll post a pic later for you guys. I'm mixing more water right now to remove the rest of it.

Your corals look to be a large size, so maybe think of what conditions they were kept before this new tank setup.
H2S can be removed from the water with activated carbon or by oxidizing with ozone. Hach makes a kit for measuring H2S, but it's best of course to reduce sediment buildup in the first place.
H2S is deadly to aquatic animals as much as carbon monoxide is deadly to humans. It doesn't take much to be fatal.
Good luck!