I’ve seen this a lot on city balconies: the furniture looks fine, but the floor ends up with brown rings because water sits around metal feet and slowly rusts them. The fix is mostly about blocking moisture and metal-to-floor contact.
Start by putting plastic or rubber glides under every leg. Avoid felt pads outdoors—they soak up water and keep the metal damp. Check the existing caps too; if they’re cracked or rusty, replace them before they mark the floor.
It also helps to lift the furniture slightly with small pot feet or a drainage tray, as long as the tray doesn’t collect water. Keep the balcony floor clear so rain can drain away, and wipe up puddles after storms. When you clean the furniture, dry the feet afterward instead of letting water pool underneath.
If your furniture is already showing rust, touch up chips and scratches with a rust-inhibiting paint made for outdoor metal. For future purchases, choose aluminum, stainless steel, powder-coated metal, teak, or quality plastic/HDPE. And if a stain does appear, use an oxalic-acid rust remover on a small test area first, then rinse well. A little prevention keeps the balcony looking much cleaner.