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In the course of 1 week, Corys seem in trouble. First my Aeneus Cory, then an albino Aeneus and now my Panda Corys having trouble swimming. The regular parameters appear just fine. I just did a 40% water change and instead of getting better, 2 Panda Corys did worse last night.

1. Water parameters
a) 80 degrees Farenheit
b) pH: 7.4 (consistent, no change)
c) GH: 30ppm
d) KH: 40 ppm
e)Ammonia .1ppm
Nitrite: 0 ppm
Nitrate: 2 ppm
(Test done with new API Master Kit, except GH, KH (API 5 in 1 test strips)

2. Tank set up
a) 17 gallon
b) CaribSea torpedo sand (white very small rounded gravel)
c) AquaClear 30
d) Furnishings: One Mopani branch, boiled and soaked three days, new with setup of tank. One Malaysian driftwood, from previous tank with Anubias and Java Fern. All new Ryuoh rocks, 4 lbs, rinsed. Airstone. Plants include: Java moss, Cryptocoryne lutea, Hornwort
e) Tanks Occupants: 3 corydora Punctatus, 4 tiny Panda, 2 Albino Aeneus, 2 Bronze Aeneus, 5 Neon Tetras
f) How long has it been set-up? 3 months, fishless cycle with ammonia. Inhabitants first in tank 5 weeks ago.

3. Symptoms / Problem description
Background: Bronze aeneus and neon tetras from small established tank, moved into new tank 5 weeks ago. All others new from reputable LFS, quarantined together in older tank 3 weeks, recently moved in 1 week ago.
A few of the corydoras, older and new have acquired a condition where they have some or all these symptoms: Lack of swimming balance, 'hyperventilating', red gills

4. Action taken (if any)
Afflicted fish is set off in separate 1-2 gallon hospital tank as needed. Fish given antibiotic dips, 4 days, then returned to tank (if he looks well - swimming, looking, eating, etc. regularly)
5. Medications used (if any)
One of the previous fish, Bronze Aeneus is prone to dropsy (at the drop of a hat... from a big chain fish store). We have medicated him 2 times previously with Ciproflaxin, 100 mg/gallon water (think this is the dose) dipped one hour and returned to hospital tank.

I don't really want to keep medicating them - I don't know what is wrong!
thanks Catfish gods

I am sorry about your fish.
I'd start first with testing the water with a liquid test kit and not strips.
80F is way too high for the cory species you have. I'd bring that down to 74-75F.
The bioload in there is on the high side with 16 fish. It's not that it's not manageable but it needs large regular water changes and better filtration, preferably external as it holds additional amount of water. Plus in a higher temp there could be oxygen problems.

The one time I've seen corys having problem swimming was shortly after I intoxicated them with an ammonia and nitrite after overwashing my filter.
The reason they did well for you in the hospital tank could be just because water was changed regularly.
Maybe there are some toxins in the tank. Pull one that is sick in another tank and do daily large water changes for it and see how it fares without meds at all, just fresh water.
I wouldn't think the water change killed your other ones unless you are adding ammonia from the tap water(if it's treated with chloramines that just break down in the tank to ammonia and chlorine without the ammonia being neutralized)
Otherwise they were probably just gone beyond recovery.

Sorry I can't help any more than that.

thanks for the fast feedback corycory.

i've turned the heater down - that could be the culprit...the quarantine tank had a different heater. this one is rated a bit high and is harder to calibrate.

also, i will do some extra water changes this week.