There's a sticky on ich treatments at the top of the newbie forum. It's not a tx I use enough to know, check! But start adding it tonight!! Maybe 1/3 dose tonight, 1/3 in am & 1/3 in pm. Or over 3 days, any level of salt will start to help. Remember to treat long enough to be entirely sure it's gone for good. 7-10 days after all signs are gone.
Salt doesn't damage your beneficial bacteria, so no worries about that. Nor dose carbon remove it . I don't use carbon on a regular basis, but if it's in your filter just leave for now.
Like plants, catfish including plecos don't like salt, but a lot of that is the rapid rise in TDS (total dissolved solids). That's why you want to add salt slowly over a couple days & remove it slowly too. If the fish seem very stressed, I would keep the temp lower than 86F, that's awfully high for most cats & just as stressful as the salt or almost. The tx might take a few days longer but, to me, it's safer.
You might also lower the water level so there's a good splash from your HOB filter, vacuum! Ich often hides in the gills & can reduce a fish's ability to get enough oxygen. The ich, salt or lack of oxygen can all cause some flashing, that's just them scratching an irritation.
Signs of a more serious reaction to temp & lack of oxygen is hanging at the surface; gill irritation, red gills or non-stop flashing.
