Fish dying looking for reasons?

[Gazbo]

I do fish tank maintenance and I have a clients tank that has a sump with 2 little giants pumps as the supply line. One pump went out and for some reason the other pump was on with the light timer and they went one night with no flow and the fish showed signs of stress lost a flame angle and his tangs started getting cloudy eyes. I got the the one pump off the timer and added power heads and a air stone to keep good water flow and oxygen while I wait for new pump to arrive. The fish are still getting sicker and received a call one tang passed and the other one is not far from it. Water test out Ok only a little Nitrates at 20 but used to to be higher than that before I took over the tank maintenance. No ammonia or Nitrite temp is at 79 salinity is1.025. For the life of I can't figure out the cause corals look fine but has basic soft corals and anemones. Snails and hermits are fine. Could this just be the result of the pumps going down and the fish couldn't recover from it. I keep maintenance equipment separate from other tanks. Haven't change or done anything to the tank been doing regular water changes.
So if you have any suggestions or ideas please let me know.

I had one other clients tank crash 3 weeks ago but think it's a separate issue over crowded tank with insufficient filter system but starting to wonder if there is a connection. I have 3 other salt tanks as clients and no problems there. All the tanks at the house are fine so I feel this is two separate issues.

 

[user 26995]

in the first tank, the pump being down. So no flow and no heat either I presume! I'd think possibly bacterial infection and stress on top of it got them. not for sure, but I believe the cloudy eyes is usually from bacterial infection. water parameters might be okay, but a bad bacterial infection can still be present and a big water change should help.

Sent from my SCH-I405 using Tapatalk 2

 

[NanaReefer]

A++ Sound advice