Limestone is a soft type of rock and will be more susceptible to damage from a salt system. The main problem contractors are seeing with salt is in the coping, beach type entries and on splash out areas. Once the pool water dries it will leave a residual of salt. You could compare it to going to the beach and taking your truck out on the beach near the water. If you do not wash your vehicle and leave the salt residue it can eventually begin corroding your metal. Salt systems are not bad products. You must keep your salt at the recommended level by the manufacture. Check your owners manual that came with the salt system. Was any type of sealant used on your limestone? That would protect the salt from being directly on the coping. Another important thing to do is keep a check on your chlorine level. The recommended schedule for testing your water is daily. However, this is not a perfect world so at least 3 times a week in the beginning would be ideal. Knowledge is your best defense in maintaining your swimming pool and equipment. Sound like to me that the pool company is attempting to remove any responsibility from them onto you. You should not have to switch over to a ozone generator to keep a warranty in force. Unless however it was in the contract and you signed it. I have seen numerous companies sell salt systems to homeowners and give them no guidance on how to operate the equipment. That is the responsibility of the pool company to disclose any information, pro's and con's, of buying a particular system. The discouraging thing is that many in the pool industry are only concerned with the almighty dollar. I hope this information helps you and I will be more than happy to help you further if I can. The previous seems very much informed. However, I would emphasis that the question is what clause are they able to point to in the warranty that says you must have an ozone generator? Ask them. They can not change (or void) the warranty after it is agreed and in force, simply because they now want to. They may refer to some clause like "...owner must provide proper maintetaince and use pool in accord with standards at all times". Well, tell them that doesn't mean install an ozone generator to...especially when the standard is to not have one...(more pools don't than do). Presuming they installed and warrantied the pool without a generator is sign enough that not having one does not limit their responsibility. If they want to continue suggesting it does, first realize that they probably ain't going to stand behind anything (for one reason or another) anyway and you really don't have a warranty you can rely on. Then demand an immeadiate refund of any amounts for the warranty they have charged already, as they themselves are saying it desn't really exist. I'll bet their more interested in keeping the money they got then getting more! Doing this by certified mail is always the best.