The rubbing on the substrate is probably an external protozoan infection. If the fish has white spot they usually rub on object. It's a bit hard to tell if the fish has white spot or just excess mucous (white marks) but rubbing and white spots is usually white spot disease.
You can treat it with heat. Raise the water temperature to 30C (86F) and keep it there for 2 weeks or at least 1 week after all the spots have gone. No chemicals needed, just warm water.
Increase aeration/ surface turbulence when increasing the temperature or using medication to maximise the oxygen in the water.
If the spots don't change after a week then it's not white spot. The white spot parasites drop off the fish after a few days and then reappear a few more days after that. The spots end up in different places.
If the spots haven't changed after a week, they are more likely to be excess mucous. If the fish are still rubbing then it will be an external protozoan infection like Costia, Chilodonella or Trichodina. You treat these with salt.
Don't use salt and heat at the same time because it can put the fish under a lot of stress.
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SALT
You can add rock salt (often sold as aquarium salt), swimming pool salt, or any non iodised salt (sodium chloride) to the aquarium at the dose rate of 1 heaped tablespoon per 20 litres (5 gallons) of water. If there is no improvement after 48 hours you can double that dose rate so there is 2 heaped tablespoons of salt per 20 litres.
Keep the salt level like this for at least 2 weeks but no longer than 4 weeks otherwise kidney damage can occur. Kidney damage is more likely to occur in fish from soft water (tetras, Corydoras, angelfish, Bettas & gouramis, loaches) that are exposed to high levels of salt for an extended period of time, and is not an issue with livebearers, rainbowfish or other salt tolerant species.
The salt will not affect the beneficial filter bacteria, fish, plants, shrimp or snails.
After you use salt and the fish have recovered, you do a 10% water change each day for a week using only fresh water that has been dechlorinated. Then do a 20% water change each day for a week. Then you can do bigger water changes after that. This dilutes the salt out of the tank slowly so it doesn't harm the fish.
If you do water changes while using salt, you need to treat the new water with salt before adding it to the tank. This will keep the salt level stable in the tank and minimise stress on the fish.
When you first add salt, add the salt to a small bucket of tank water and dissolve the salt. Then slowly pour the salt water into the tank near the filter outlet. Add the salt over a couple of minutes.
