Cyano deaths?

[Murminator]

I am thinking it is a combo of cyno, red slime remover and 1 of the fish dying caused a huge chain reaction. Not sure if I can rule out tap water problems. I was a firm believer in tap water. I have had dinoflaggets before and hair algae in different tanks but I blame that on summer time and not keeping up with maintience. I have also done numerous 75-90% water changes on salt tanks packed with coral with tap water with no ill effects. I have been tap water for 30 years At 1 time I was running 10 tanks on on tap water 3 of them saltwater all treated with prime. Now I am down to a meer 6 tanks and in 1 on salt which is RO/DI. As for the 1.1 phos it was before a a water change with a dirty filter sock and filter floss which i was using to polish the water a bit.