I have a Morebeer stainless steel 9 gal. economy brew kettle. I have brewed 8-10 batches of beer in it over the last year or so. I noticed after my last batch that just around the "boil line" it appears to be getting pitted. There are little black dots. They are very small but I can just start to feel the roughness when I rub my hand over them. There are also very large "pit" marks where the couplers were welded in, they have been there since I purchased it. I have read that the kettle should not be cleaned with bleach, so I have kept that away from it. I always clean and dry my kettle right away after a brew day. Please help me figure this out. Thanks.