I have a 30 year old galvanized steel wall inground pool, Clayton and Lambert. Replaced first liner after 18 years. Small amount of rust at that time which I removed and repainted before new liner went in. Time for another new liner, walls have much more rust now, even a few holes, size of pencil lead. I am concerned new liner will out live the walls with the way the rust is coming on. I had planned to grind some of the rust off, paint the walls with Rust Aim Primer which is suppose to have a chemical reaction with the rust and stop it. Do you have any ideas on repair of the walls or some sort of patch system for my situation?

After you clean the rust by grinding and wire wheel, you can patch holes with epoxy. The easiest to access and use is probably Bondo. You can get it at auto supplies, and sometimes at building supplies. It is used most of the time to patch holes in sheet metal on cars. Don't try to just fill the hole. Spread it on an area much larger than the hole so that you can "feather it in" on the edges.

It is important to get off all of the rust, or get it neutralized. Sometimes a product that has phosphoric acid is helpful. It doesn't always seem to work though, so you may want to try a test area before doing it all.

After you wire wheel, grind, and patch. Then a good coat of primer, and a heavy coat of rustoleum paint should help you get some more years out of it. A word of caution... you'll need to let rustoleum cure for several days so that the liner will not stick to it. If you need it to dry more quickly, you'll need to look at either spray paints, or an automotive paint. I prefer rustoleum because it is very high in solids, so you can put it on heavy with a roller, airless sprayer, or brush. And, it holds up very well.
Al

I think Bondo isn't going to perform well around any rust and below grade. I would buy some thin sheets of galvanized tin and epoxy this sheet metal over you bad areas. This pool will not last forever and when the sheet metal fails you will be old. Even concrete pools don't last much longer than 30 years.

ballengerb1 has a great solution. Be careful to get the edges stuck down good, or it may cut into the liner.

Yep, if I forgot the details I'd recommend trimming the corners into small arcs and then a quick pass with a file. This does remove the galvanized coating on the edge but it will last you a life time, assuming you aren't 10.