When I first had my pool before I found this forum, I used Trichlor pucks in a floating dispenser and it parked itself by stainless steel bars in my pool. The acidity and high chlorine levels form the pucks rusted the two mounts closest to the feeder and I still live with that rust to this day -- it's a reminder to me of the hazards of using Trichlor pucks near surfaces that are sensitive to acid or high chlorine levels. Vinyl liners are sensitive to acidic conditions in particular while the high chlorine level may bleach out the color.