Cyanuric Acid IS an acid. It is not as strong (by weight) as Trichlor (and not even close to Muriatic Acid) and fortunately it dissolves slowly, but if it is touching the liner especially on the bottom where there may be poor circulation, then it can be harmful locally. Perhaps it would only be a problem if this were done repeatedly, but it's best not to take the chance and to use the nylon sock instead.