Hi Leandrah,
Thanks for using the questionaire here and the pictures. Im guessing based on how long your fish have been dealing with issue that they probably have flukes. These are very common in discus and unfortunately very hard to eradicate..
The polyguard you are using should knock them back in numbers but because of their lifecycles they tend to spring back up.
Having a tank with substrate makes treating parasites more challenging as well.
Did you see any improvement at all with the Paraguard?
There are several treatment choices for dealing with flukes to consider. The first one I would suggest is a course praziquantel..Though their have been cases reported of resistance to the med...its generally an inexpensive and safe medication to use that is highly effective on flukes. I would only use pure praziquantel. You can find it at places like jehmco.com That would be my first suggestion if the polyguard does not work for you.
This is unrelated but I would also suggest that you bump up your feedings to at least 2 times a day or more. Your smaller discus will benefit greatly from it.
hth,
Al