2 fish dead in one day

So this week my main return pump died (realized it on Tuesday). Still had my chiller pump putting water into main tank. Couldn't get a pump till last night an hooked it up. The only other thing I did was add again some media as I have been battling phosphates. This morning early noticed my Tomini tang and fox face were breathing heavy. Now this afternoon my Tomini died and looks like by the end of night my foxface will be gone as well as he is in deaths corner, the corner all fish in my tank have gone to die in.

Not sure if it is an oxygen issue that try couldn't overcome, tested parameters and they seemed ok. Salinity is fine. Not sure if I didn't rinse out media enough before placing it in and maybe something clogged up their gills, media has been used so it wasn't a new addition...stumped at the moment.

 

How long was the return pump out?I am assuming you have a sump.If the water stopped circulating through the sump it is possible the water was fouled and/or your biofilm died and caused a mini cycle to occur.