Rust on aboveground pool walls is common, especially after a few years. Any spot where water may seep through the liner and onto the inner walls can eventually cause rust to develop. If the rust is not removed and the spots repaired, the damage will continue to spread and eventually ruin the pool walls.
Remove all ladders, gaskets and face plates from inside the pool. Drain the pool completely. Remove clamps, pool ledges or top plates that hold the liner in place and then remove the liner.
Locate all sources of rust on the inside wall, taking time to walk around the entire inside of the pool. Check for rust around all bolts and seams as well as obvious patches of rust on wall panels.
Brush larger sections of rust with a wire brush. Be careful not to scrape, but rather gently brush off little chunks and pieces of rust.
Sand all spots of rust with light pressure. Go over each area several times thoroughly to remove all the rust. Repeat on the exterior (outside) walls of the pool.
Tape any obvious small holes that were caused by rust in the walls or seams. If a hole is bigger than a silver dollar, cut a small piece of metal to size and insert it in the hole. Then tape over it with duct tape, making sure no metal is sticking out that could puncture the liner. Place the tape neatly and overlap a few layers to completely cover the hole, with at least 2 inches of tape extending beyond the hole.
Spray over all sanded and taped areas where rust used to be with enamel or a Rust-Oleum-type product. Allow it to dry according to the manufacturer's specifications before you replace the liner.