Stainless steel pool ladders that have rusted or pitted are often a result of low ph in chlorine pools or too much/too little salt in salt water pools.
Types of Stainless Steel: There are 2 main groups of stainless steel that your pool ladders could be made from. If you have a salt water pool you should have "marine grade" type 316 stainless steel ladders to prevent rusting. They do cost more, however the added corrosion resistance is the only way to go for salt water pools. Read more about Why Is My Pool Ladder Rusting?