One of my seven kuhli loaches just died. I am not sure why and would like your insights. Here is what I wrote to post as I first observed the problem about an hour ago (sorry for the length; it's an amalgamation of three shorter posts I wrote on a local aquarium forum):

A short while ago I noticed that one of my loaches was writhing around in a manner distinctly different from the "happy kuhli dance." It then draped itself passively a few places in the tank, panting heavily, and was fairly easy to catch when I removed it.

It has a whitish-grey area on its side -- more on the right side than the other, and it looks like a circular spot on its back where the paler spot spreads out from. It's belly seems swollen and there seemed to be some substance peeling off from its underside. I'm wondering if that circular spot is a bite mark. The tank has been a bit more aggressive in the last two days as the new female GBRs settle in. This loach was hanging out in the upper greenery where two of the new fish were hiding.

If it's not injury, then likely it's a parasite or bacterial infection of some sort. I have maracyn, maracyn 2, and maracide available. If any of the other loaches show similar symptoms, which of the meds should I use? Do I cut the dosage for loaches or is that just when treating with salt?

Tank details:
- planted with a sand substrate
- river rocks and driftwood but no other decor
- 50% water change last night
- water parameters are currently: pH 6.6, ammonia 0, no2 0, no3 5, 80F (There was a bump in the ammonia to 0.25 or a bit higher prior to the water change. I added three female German Blue Rams on Friday last week.)
- 25 gallons
- two filters: Aquaclear 50 and Aquaclear 20; the 20 was added to the tank setup with new media when I added the three new fish, so it's been running only a few days.
- tank has been cycled with the Aquaclear 50 since mid-November.
- two pearl gouramis, four GBRs, and seven (now six) kuhli loaches (2 striped).

I've been trying to inspect all the remaining loaches in the tank, but have only been able to see five so far. One of them has very red gills and is red around the anus area; two of them have redder than usual gills. All of the other fish look fine.

I have a 5.5 gallon hospital tank set up with heater and filter but have not put any meds in yet.

I'd appreciate any advice you have to offer.

photo of the loach that died while it was stil in the main tank:

photo of one of the black kuhlis with very red gills:

of two striped kuhli loaches with red gills.