oh boy dying koi, angelfish that is

Per sticky#2 format:

1. 90 gallons
2. Water parameters just checked : GH 8 dH, KH 6 dH, pH 8, temp 80 degrees, NO2 is a hair over 0 mg/l, NH3 0, CO2 about 1.8 mg/l.
3. Fresh water
4. The tank is well established @ 8 months.
5. loach, pictus catfish, pleco, 8 tetras, dwarf gurami, 8 snails, 5 small angels (marbel, yellow and 3 koi).
All fish are medium except for small angels.
6. no quarantine tank
7. 80 degree temp ( I live in Florida)
8. 90% plant with driftwood piece (eventually moving to 100% plant). Gravel is pebble, florite plant gravel around live plants. {What can I say? I originally did'nt think I'd do natural plants, but I'm now facinated by them.
9. 405 Fluval filter (lovely system)
10. none
11. Lighting goes from sunup to about an hour or two after sunset.
12. I gravel vac 30% every other week.
13. I feed daily, but not much. Tetracolor flakes mainly, Spectrum cichlid food at times.
14. The koi were recently purchased two weeks ago. They weren't sickly but they weren't go-getters either.

Here is the problem cichlid below.


Here is one of the healthier koi angels



Here is a very healthy yellow angel



I was told the red gills are normal for koi angel fish, but somehow I suspect that may not be true. Any thoughts on what might be the trouble? It's a pretty koi, but I suspect bad stock.

I just bought the koi angels about two weeks ago.

Sorry guys, the koi died. Thanks for the input. The other koi lived and is thriving. My small angels will be with me for the next few years, so I'll write this off to stress and slightly high end pH. Even though this is a 90 gallon tank with a modest population, I think it just too difficult to maintain several angels in one tank. (They are gorgeous, but can be a bit mean to newcomers.)

I love this website.

P.S. We need an emoticon for R.I.P., perhaps a packman toilet bowl.