HELP! NastayNatron's tank

[Lampshade]

One thing to make sure is that all the pumps are on and circulating water. Odd to lose fish from much more than the basics of water movement and temp/salinity. So as long as there isn't a pool of water on the ground, salinity should be the same. Temperature is easy to check, so just make sure there's lots of water turn over.

Did the skimmer cup overflow into the tank? that would cause it to be cloudy and also cause a nitrate spike, starving oxygen.

Did a pump fall off a mount and blast into the sand? that could release all kinds of nasty stuff into the tank.