You may also find that that female is unable to swallow food and ends up spitting it out. What happens in that case is that so many flagellates inhabit the throat surface (having worked their way up from the intestinal and stomach lining), that that epidermis becomes inflamed and swollen.

The small spots on the fins could be Ich or velvet or another parasite. Please Google images of those diseases. Also check the section for all three of these diseases in Immediate Help (link is in the upper right of this page). Fin rot and all of those conditions are “encouraged” by stress, often in the form of less than ideal water quality and sometimes dramatic changes in temperature. Both for the sake of your “afflicted” guppies and the others, please try to do more partial water changes. (Easy to say, hard for all of us to do.)

Guppies are best off to the basic side of the pH scale (say 7.2 to 8.6). Since most municipal water is (by code, law, EPA edict or something) buffered to the alkaline (base) side so that old lead pipes will not dissolve in the drinking water. pH is seldom an issue. However a lot of decaying organic stuff (uneaten food, dead plants, fish waste, a body behind the filter) can cause a pH plunge. (See Acidosis in Immediate Help.) That is one of the many reasons why we strive to keep up the partial water changes.

That will help the immune systems of the other guppies to resist those maladies (which are often present in aquariums at “non-lethal concentrations”). It may also help the guppies having problems.

If you can establish what the spots are and can treat that fish in separate quarters, go for it. I would also do that with the guppy, which perhaps has Hexamita.

Medicating in the community tank (especially if antibiotics or organophosphates are used) may partially or completely kill off ALL beneficial bacteria which keep the nitrogen cycle going. If you have not other place to medicate, try increased partial water changes. (Right now draw some water into holding containers, treat them and let them sit over night open to the air.) If you must treat there, understand that the tank may become very high in ammonia, especially since we must also remove any activated carbon in the filter. Feed little. If you can, test for poisons like ammonia, nitrite and even nitrate.

Because of what happens to the regular tank, it is best for the healthy guppies and other fish to treat elsewhere. That keeps them from becoming so stressed that their immune systems can't resist illnesses.

A hospital tank can be started with some gravel from a healthy, established tank. (I'll take one out of two.) If a box or sponge filter can be run in that regular tank for a couple of days, the filter and maybe 50% of the water in the hospital/ quarantine tank can help import a nitrogen cycle to the treatment tank.

Metronidazole (Flagyl for humans) is often used in treating for Hexamita. As an antibiotic, it is less devastating to the nitrogen cycle than many treatment. I was also surprised to read that it is very effective against anaerobic bacteria. Also look at the discussions of Metronidazole baths in the Immediate Help section on Dropsy/Bloat/Protruding Scales/Swollen abdomen.

Not even being able to guess what the spots on that other guppy may signify, I can't make treatment suggestions beyond increasing those (!@#$%^&&!!) partial water changes. Doing water changes consistently is the most difficult part of the hobby for me too.

Recently I won a package of Jungle's Parasite Clear (one of those fizzy tank buddies) in a “goodies bag” or sample bag a some aquarium club function. Like many commercial treatments produced by the aquarium industry, it contains several substances, which are supposed to treat several maladies. Its active ingredients (remember I am in not way a medical person) include Praziquantal, an anthelmintic effective against a number of internal and external parasites (NOT Cammalanus worms though), Metronodazole, the antibiotic already mentioned above, Acriflavin, a medicinal dye used in treating velvet (perhaps disrupting the photosynthesis in the velvet or Oodinium/ Piscinoodinium) and Diflubenzuron, an insecticide (which I don't know much about) used in a lot of treatment.

That might be worth a try, certainly with the guppy with the stringy feces. If it doesn't effect a cure for the spotted fish, used water changes and activated carbon filtration to remove all of that stuff before trying again.