Need AC in SW Valley

So over the last few hours we have had most all our fish die and coral is retracting. We are still searching for for foreign contaminants and I'm starting a 55g water change (300g system) but I'm down to a few cups of AC and stores are of course now closed. 

I have some ac you can buy from me or replace later. I live in murray

Observation that may or may not matter. The macro in my sump is thinned out a lot. Where I normally might toss out 1G a month or so, I probably need more right now.

What type of heater are you using? Is it possible that your tank overheated? The macroalgae dying back could be symptomatic of overheating or contamination. Is it possible that kids put something in the tank or sump. Stray voltage only kills fish that dwell in the rocks or substrate. Or are sleeping in the rocks but it doesn't happen that quickly unless it's a lot of electricity. Your alk being low wouldn't kill you fish quickly either unless it was super low and you had a major pH swing.

Sorry for asking for help and then ignoring the thread. Best guess is it was a cuc-nuke. Lost a few handfuls and have 4 left. Thanks all for the ideas.