Disease affecting white clouds?

The parasites in your swordtail expelled the cysts (eggs) threw the feces and they dropped to the gravel. They have now become adults and infected your white clouds. Since this is a plant tank I would recommend removing all of the fish to the quarantine tank and treat them there and keep them there for at least 20 days. This should be long enough to rid the main tank of the parsites because they don't have a host. I don't know what types of plants you have though raise the temperature to the highest level that will not damage the plants and leave the aquaium at the temp for the 20 days or longer. During this period siphon the substrate on a regular basis. They key is getting the cysts out from the top 1/4" of the substrate. Do not use this same tube on both aquairums because you do not want to contaminate using the same nets, etc. Since you have a quarantine aquarium you should have 2 sets anyway. Good luck though get started ASAP.

I think you should stick to just doing a 25% water change every week. This ensures that most of the live bacteria is saved and can continue growing and populating the tank once the new water is introduced. The water seems fine, although this could be that there is not enough oxygen in the water.

Do you have an air stone? This will help, considering it puts oxygen into the water. Although, the white clouds could just be getting used to the water, or they could be infected with parasites themselves. It's hard to tell at this point, but be sure to make those small changes before doing anything drastic or jumping to conclusions.

Any time a fish gets sick, there is high probablility the rest of your tank is infected. Treat your whole tank with the same medication you used for your swordtail, and see if that doesn't do the trick. Good luck!