I'm glad it appears to have worked!
Just be aware that Seachem Paraguard works on external parasites only - not internal round/flatworms, and white stringy poop usually means round or flatworms. So just keep an eye on him, worth researching the signs and symptoms of internal parasites and monitoring him a bit more closely for a while, you know? the increased water changes almost certainly helped as well. Very few things can't be improved with improved water quality.
But I'm crossing fingers for you that it's all good now! Appreciate the update too, always good to hear a happy ending, and when people take the time to come back and let us know how things went.