Don't add chemicals to a tank unless you know what the problem is.
If you had a Betta that got small white spots on its body and fins, it probably had whitespot and Paragard would work because it contains copper. However, the platy does not have whitespot.
The white patch on the platy could be colouration, excess mucous or a minor fungal infection. Paragard won't treat any of those things.
Don't give fish dips/ baths because the stress of catching them, lifting them out of the water, putting them into a small container of chemicals, then moving them back into their tank can harm and stress them. And moving pregnant/ gravid livebearers is even worse because you can rupture the sac in her abdomen and kill the babies. Chemicals can also affect the babies that are in the female.
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The best treatment for most fish health issues is big daily water changes, gravel cleaning the substrate, cleaning the filter and salt.
If you can only do a big water change once a week, then add some salt now and do a 75% water change and gravel clean the substrate on the weekend.
Wipe the inside of the glass with a clean fish sponge.
Clean the filter if it hasn't been done in the last 2 weeks. Wash filter media/ materials in a bucket of tank water and re-use them. Tip the bucket of dirty water on the garden/ lawn.
Add 2 heaped tablespoons of rock salt, sea salt, or swimming pool salt for every 20 litres (5 gallons) of tank water. Keep the salt in there for 2 weeks.
If you do water changes while using salt, add salt to the new water before it's added to the tank.
