Fish dieing

Question
QUESTION: I have a 55 gallon South/Central American tank.  It has 1 angel, 2 german blue rams, 4 black and 4 red phantom tetras, 5 green fire tetras, 3 cardinal tetras, 3 otos, and 5 guppies left.  Today I lost an additional 2 guppies,1 cardinal, and 1 greenfire.  Yesterday i lost a cardinal and a guppy.  Before that I have lost a couple guppies, a couple rams and angels.  The angels rarely last more than a couple days...the rams I had a little over a week and the other a couple weeks.  One cardinal tetra lost 1/2 of the blue on it's body (dorsal fin to tail) and was very dull on that half.  The front half looked normals.  The angels usually hang at the top when healthy but stay at the bottom when sick...they also lose ability to swim and have trouble staying horizontal.  the rams usually hang out at the bottom, but go to the top when sick...they lose ability to stay horizontal and one looked fatter than usual (both had clamped fins).  The guppies seem to be bloated.  

my tank has been up and running for 2.5 months..it was seeded with bacteria from another established aquarium.  Ammonia is 0, nitrite is 0, and nitrate gets to 5 after a week.  I had been feeding a varied diet 2X per day...am switching to every other day.  Temp 80* and ph 8.0
ANSWER: Jamie-
Sorry to hear about your fish.  Your pH is very high for fish of this type.  Rams and cardinals in particular prefer water in the upper 6s, and you're at 8.  Rams and angels are extremely sensitive to pH.  They were probably very stressed, combined with the fact that the angel was probably chasing the tetras, which explains why one of your tetras is losing color.  I'm willing to bet that that is the cause for your troubles.  My advice would be to try to lower the pH.  Don't use chemicals because they're costly and add up as you do water changes.  Peat moss should be availible at your LFS, and just put a bit into your filter.  It'll drop your pH to the lower 7s, which should help recover your fish.  Put some aquarium salt into the tank to destress the remaining fish.  Also, continue to do water changes.  The bloated guppy implies that there may be some unsafe bacteria in the tank, and the stress levels of the fish made it more susceptible to infection.  Perhaps some Melafix may also be in order.  Try that out for a few days, and follow up with me.  Good luck.

---------- FOLLOW-UP ----------

QUESTION: The rams were bred in a pH similar to mine in Florida.  The angels were also bred in Michigan in a pH of 8.  The angel is rather small and totally ignores the other fish.  The fish store also keeps the fish in a pH of 8.5.  I am very specific in my acclimation process, using an airline tube to drip my aquarium water into a container over the course of 2-3 hours after which I float them in said container in water for 15 minutes to equalize temp.  I also dump part of the water out of the container periodically in order to reduce the ammonia build up from the waste the fish produce in the small acclimation container.  Up until a week or so ago i did not lose any fish.  The angels and rams, guppies and tetras all looked very healthy and unstressed.  What I *think* happened was that I introduced a couple cardinal tetras and a green fire that looked ok in the store, but when I put them in my tank, they looked rather emaciated and the two cardinals died within a couple days and the green fire died today, still emaciated after 2 weeks of good feeding.  It was shortly after adding these two fish and another ram that began to look emaciated that the deaths started happening.  That is why I am leaning towards some sort of disease/parasite/bacterial infection...but have no idea what.  There are no outward symptoms...and the only sign that I've seen in the bloated belly on the guppys and the emaciated cardinals/green fire/and one ram...what should I treat the tank with other than melafix which I've had family have bad luck with?  Should I try a broad spectrum antibiotic such as a marcyn/maracyn 2 mix...or some other form of treatment?  Another thing I was curious of is if my feeding schedule could be hurting the fish?  I feed pellets/flakes 2x per day and 1-2X per week either freeze dried blood worms or frozen brine shrimp.  Could this cause this kind of response in my fish?  What could have cause the cardinal to lose color in only 1/2 of her body?  that seemed very odd to me?  Thanks for all of your help.  

Answer
With your added analysis, I have to agree with you, perhaps an internal parasite.  Try not feeding them for 2 days, along with an internal parasite medication, perhaps Pimafix or Para-Chem.  Using some aquarium salt will cause parasites to bloat and fall off, if they are indeed the cause.  Give that a try, and let me know.  I'm very curious.  Keep me updated.