losing my angels

[3dees]

yesterday I noticed my flame angel was staying in the cave. he came out when I fed but only ate one Mysis shrimp then went back in the cave. this morning he was dead. my midnight angel was fine but today he is in the cave doing the same thing. he wouldn't come out to eat. checked my water and everything is fine.
ph 8.2
salinity 10.24
ammonia 0
nitrites 0
nitrates about 5ppm
I did notice my kh was low at 6. no signs of anything on the fish. no aggression. they were in the qt together and added to the dt at the same time. in the dt for 2 weeks. fish were two inches each. tank is 120 gal. fowlr with 140 lbs. of lr. one fish I could understand, but two in two days? all other fish in the tank are peaceful. no tangs, triggers, etc. they are all fine. any ideas?

 

[becca10]

Are you feeding them sponge?

 

[Eienna]

How long did you QT?

 

[Alesolra]

Fish do not need the KH. That's just for corals

 

[3dees]

didn't think kh would have any effect. I feed them different frozen and dry foods including frozen angel food. they were in qt for 4 weeks with a round of prazi pro. can't figure how they go from acting normal one day and dead the next. the midnight is still in the cave, but I'm half expecting him to be dead in the morning. it's exactly what the flame did. I'm starting to regret giving up my discus tank.