Disastrous day!

[Gordi]

It all seems far more complicated than I expected. I did test ammonia levels after the first emergency water change and the level was off the scale. It's been tested every morning since Saturday and has been gradually coming down until this morning when ammonia and nitrites are again reading zero. I'll get some photos when the lights go on again (if you can see past the hair algae).
Thanks very much for your input!!

 

[brandon429]

the pictures will help agreed.


to show you how ammonia misreads go:

Sustained Ammonia spikes are misreads

The reason you think your reef tank can’t control its ammonia is due to false training from old cycling science. That and you don’t own a seneye on the tank in question: if you did, you wouldn’t ever think your ammonia was out of control...

www.reef2reef.com

the chance that your ammonia crept up before the fish loss is zero percent, or, we'll have the first entry we can record there above for such an event.

key claim: must be a digital measurement to qualify. we show in links there how non digital kits cause exactly your issue for pages on end. it's not that your ammonia is still high, and slowly coming down...it doesn't work that way in reefing but only digital measurements show this truth. your pics will show the surface area details that help you eliminate ammonia noncontrol from all future loss hunts

the main takeaway from that thread above: nobody has an ammonia noncontrol issue. any seneye owner can see this easily.

I once sprayed Sprayway glass cleaner on my tank to wipe glass and it immediately killed about 15 freshwater fish, no doubt there are home contaminants that can zap fish.