I recently purchased a new pleco that was sold as a "Spotted Pleco" and the person at the fish store didn't know much more. The spots are off-white/yellow-ish. Not sure how old the fish is, guessing fairly young as it's about 3.5 inches now.
Pictures are attached... they're not the best quality as they were taken with my phone.
I've never had a fish with ich before... thank you for pointing that out. I might not have noticed until I put him in my big tank and all the fish got sick!
Best thing for me to cure ich has always been increasing the temperature to 34 or even 35°C for like 5 - 7 days.
But I only keep plecos, which got no problem with these high temperatures.
So first check if all your fishes can live with 35°C and if so once you increase the temperature, put in an "air stone" (or however this is called in english) to get some more oxygen into the water. Very important with these high temperatures!!
I've never tried to cure it with medication. Don't like that stuff since it stays in your water and specially filter even after many water changes and filter cleanage.....