losing fish rapidly... HELP

im stumped without all params..

 

20-40ppm nitrate seems high for a tank that's been up since september. How much live rock do you have?

What size tank is it. Perhaps it just overstocked. You could have exceed your tanks filtration ability by adding the tang.

Re-test Nitrates. Add some Seachem Prime per instructions if they are high.

 

I would suspect the new powerhead is leaking voltage.

 

+1 for this if the fish went downhill so fast. Did the angel show any signs of distress prior to finding him dead? Also not sure if you said, but what size tank and do you run a skimmer to oxygenate the tank?

 

I would like to help- try this:

What have you changed as of lately?

What have you done lately that might effect you aquarium?

Do you have coral in your tank- if so, does it look normal?

What equipment are you running? Is any of htis equipment amiss?

Water quality- so important, from what you have been telling us- I suspect a large ammonia spike, and high nitrates, but I could be wrong.