It will probably be sufficient. Metro isn't the strongest antibiotic but it's good for parasites. I'd give it at least two weeks to know if it's working. Kanaplex as a bath would be better for bacterial infection but it's kind of a crap shoot at this point knowing what's the underlying issue unless you can find evidence it's one or the other. Like if you feed live food I'd assume it's parasite.. or whatever else you can come up with. You can also feed metro and bathe in kanaplex at the same time but it can be pretty stressful on the fish, so I don't know if I'd go that route unless I was feeling desperate.
If you're feeding the metro then make sure that your infected female is the only one that gets it, or if you suspect others may have an infection you can just feed the whole stock. It wouldn't hurt but I wouldn't feed fish that are fine because you don't want it to be ineffective because of overuse if you actually run into a problem later on down the line. I wouldn't medicate the whole tank with Kanaplex unless again you feel the rest have the same problem. You can get a gallon or two acrylic container, fill it half full and it should float in the larger tank or if you have a hospital tank you can keep warm another way that'd work too.
Seachem makes some: http://www.petmountain.com/product/m...le-5-gram.html
You can get it any place that sells Seachem products. What I do when I mix it up is also get a tube of focus http://www.petmountain.com/product/b...hem-focus.html
, which is a binding agent and helps the feed be more effective: It isn't necessary but it should help.
I use garlic guard http://www.petmountain.com/product/a...lic-guard.html
(it's garlic juice extract with no extra additives or preservatives) but you can also use a little tank/dechlorinated water. Put a little of the liquid of your choice in a cup along with one scoop each of the metro and focus. Mix it up really good then add few good soaker pellets in them (wheat based ones you wouldn't usually feed your fish like Hikari) and mix that all around. Let it soak 10-15minutes then feed two twice a day. I mix it up fresh every time I feed but you'll have to mix it up fresh at least daily. If you choose to only mix up once, cover it and place the rest in the fridge. Before you feed a second time in the evening, bring it out and let the mixture come back to room temp. At this point they will no longer float so make sure to remove any uneaten from the tank.
The Gold Fish connection also sells some medicated feed but they're large so you would have to crush them and my fish didn't like the taste: http://www.goldfishconnection.com/sh...php?parentId=5
The medi gold is for bacterial infections and contains Ormetoprim, Sulfadimethoxine, Kanamycin and Oxolinic Acid. Metromeds has Metronidazole, Ormetoprim-sulfa and Oxytetracycline - that's the one you'd want if you wanted to try. It has some antibiotics and metro which could work on parasite.