Help!.. Genocide, Julidochromis self destructus

90gal, aquaclear 500, cycled, 1 yr running with
small airstone with a small airpump.

3 p. Zebra 3"
2 Red Zebra 1"
1 yellow Lab 3"
2 featherfin catfish

10 Julidochromis transcriptus gombi.

Eventually the Julies multiplied and multiplied, at one point I had
almost 50 including about 12 babies.

I went on vacation, let someone take care of fish, when I came
back there were 3 or 4 julies lying dead on the bottom. Some
had been partially decomposed and were wrapped around the
filter intake, but filter was still flowing.

I immediately removed the dead ones, but ever since then 1 or 2
are dying every day for over a week now. I do 30% water changes
every 2 days, that didn't help a bit. I always age my water 24hours
with an airstone in a big 55gallon bucket. All the Julies keep dying,
there are only 5 left. Strangely enough none of the other fish are
dying, but they don't seem happy.

What is going on I've checked the water 3 times this week and keep
getting good numbers, here they are.

PH 7.8
Ammo 0.1ppm
NO2 0.1ppm
NO3 5ppm
GH 80ppm
KH 50ppm
temp 77

Could the dead cadavres cause the water to be poisoned but not
measureable on any of my testers?
Could the Ammo spike have happened already and as a result fish
die weeks later?
Are the Julies wealer fish or are they genetically weak from inbreeding?
None of the other fish are dying. Any help would be greatly appreciated.

....Kodiak