First Loss!

Hello,

Well, I had my first "fish loss" today - one of the juvenile angelfish
was swimming on its side, and then upside down, this AM. I moved it to
a quarantine tank to observe and try to treat it, but it died before I
had a chance to try anything. No sign of trauma or attack.

I've checked water levels (I am due to water change today), and they
are at 0-0-20 (ammonia, nitrite, nitrate), with a seemingly-stable pH
of 7.0. Water is quite "soft" in both KH and GH. I have been changing
about 33% each week when I gravel-vac. My last water change was 6 days
ago - right before getting those new angels. The only thing amiss
seems to be water that is slightly white/cloudy.

Since this is a relatively new tank, I am concerned that something is
wrong. It seems to have cycled OK (I added BioSpira 1.5 months ago to
speed it up), and I have added the fish slowly. I have been checking
ammonia-nitrite-nitrate and pH levels daily. The other fish seem fine
- one other juvenile angel, 6 cory cats, 2 full-size male dwarf
gouramis, and 3 juvenile female dwarf gouramis. Everyone is eating -
frozen bloodworms, brine shrimp, and flake/small pellet food in
rotation, along with sinking carnivore and algae tablets for the corys.
The only threat to the angels would have been the dwarf gouramis, but
they ignore each other totally from what I have seen. (The gouramis do
tussle with each other, but nothing serious.)

I had had the juv. angels for 6 days. (They were/are about 1-in. in
body height). They were tankmates at the LFS - I have not observed any
aggression between them. I am not sure how long they had been in the
LFS, though. Maybe new arrivals? I know Internet diagnosis is rather
silly, but I can't resist! Do you think it was probably something
wrong with the fish - or my tank? :-(

Thanks for any insights,

- Lisa