Southern platy fish with white stringy poop, not eating and staying in the surface

Intestinal worms in fish don't come from plants. They come from Asian fish farms that regularly grow ornamental aquarium fishes in sewerage ponds, or they grow daphnia (small crustacean) in sewerage ponds and feed the daphnia to fish. The fish get worms from eating the infected daphnia and pass it on to each other. The ponds containing fish have the fish removed and sold before more fish are added. So worms and worm eggs are left in the pond to infect new fishes being put in the pond to grow. Most aquarium fishes coming from Asian fish farms are regularly exposed to, and or infected with intestinal worms.
thanks Colin, this is very helpful, again, I feel that asking for info to the fish keeper in the shop is not helpful at all :(. Do you think they can come from snails? or its exclusively from this Asian ponds from daphnia?
thank you so much... so far both platies are alive, and I am very grateful to you all your help, as i was able to act quick! One of the platies still skinny, but I think she's recovering.

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