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.

 

[spieszak]

power heads pointed at the surface? Tangs are oxygen hogs... as much gas exchange as you can

 

[Gazbo]

Yeah I still have 1 supply pump that's aimed at the surface and on the opposite side I put a air stone deep in the tank and added 2 per heads for water movement. The tank has no water movement other than the 2 supply pumps in each back corner. Been trying to get them to add more flow with little success. Maybe now they will after losing there prize fish. I just leaning on the side that with the pumps going down overnight that was enough to kill the angel and stress the tangs out enough to where the slowly passed. I just want any opinions of things I might be missing.

 

[Gazbo]

Ok got new pump on everything is as it was the fish have cloudy eyes he lost a flame angle, 3 royal gramma's and a large tang. The appear to have cloudy eyes and a little pale is this from no water movement in the tank or should I be looking into another reason why the fish are getting sick and dying. The only fish left are 2 clowns with a little cloudiness in the eyes but look and breathing fine. The other fish is a Naso Tang he has cloudy eyes and pale colored skin.

 

[fulkerl]

Are the pumps submersible? Just thinking it may of melted down and leaked copper, chemicals, ect into the water.. maybe running carbon will help. How's the ph level?

 

[Gazbo]

There external pumps I am running carbon as a precautionary. And haven't tested the oh will do that today