The best way I find is to boil cloves in a pan of water for 10-15mins then allow to cool (you can use clove oil but I have only used actual cloves myself). The mixture is then gradually added to a small tank (1-2gal) that the fish is being contained in. You will gradually see gill movement slow and eventually stop. I have heard of people delivering a short hard blow to the head, and also there is a freezer method which most will agree is inhumane, the clove oil method is best by far.
I personally would not have put her tank mates into quarantine with her if they are showing no sign of illness. The idea is to prevent and to isolate what she has. You have the right idea in decreasing light and providing her with plenty of areas for cover
If it is a build up of fluid, Im not to sure what way you would go about treating it, in other fish (ie not loaches) I would use salt to aid osmoregulation but imo salt and loaches do not mix so thats out the door. If the fluid is a result of a bacterial infection I would think your best bet would be getting hold of some antibiotics-Im not to sure what brands/names you have them under were you are (Im only familiar with UK brands).
Do you see her poop at all? if so, normal colour etc? Bit of an odd question but it would be an indication that her internal organs are functioning well.
Not to sure what else to recomend at the moment, hopefully someone with a bit more experience will be able to chip in with some ideas.
As long as shes active and eating I would try and treat her with what you can and hope she pulls through
Edit;
Would it be possible if you could post up tank parameters (ammonia, nitrite, nitrate)
Ashleigh
