Lost Angelfish

[Medkow74]

Hello all. Sorry if this is in the wrong channel, I don't know if there is a disease involved or not.

So I lost an Angelfish suddenly today, seemed okay yesterday. No signs of disease or abuse.

I just tested the water

Ammonia 0 ppm

Nitrite 0 ppm

Nitrates between 10-20

Chlorine 0 ppm

GH 300 ppm

KH 80 ppm

PH 7.4 or 7.6

Would GH or KH kill a fish? The only other thing that changed and it was last Friday, I added two Super Red Long Fin Plecos. Would they attack Angelfish or any fish?

Thanks any help would be appreciated since I have two more Angels in the tank, they seem fine as well. Forgot it's a 36 Gallon tank.

[FrozenFins]

not sure what could have happend. you parameters seem fine for an angelfish. These deaths happen where their fine one minute and the next mintute their dead. He probably didn't have a disease if he was fine and eating healthy the day before. Angelfish have been knows (especially wild caught ones) to run into the glass and kill themselves, idk if that was the case, it could have been. It could also just be old age, angels live to 5 years ish. If you got him from a store you wouldn't know how old he was unless he was a baby.

[Medkow74]

Yeah he was pretty young when I get them in July. Probably half dollar size now. 

I realize I won't figure why it died. I just wanted to make sure parameters seemed good. If they weren't then I could do something to stop the others from dying. 

I do have a bunch API General Cure. Do you think it would be worth using a couple dosages?