If your tank is sitting for a while between uses then you need to remove the swarf at the tank bottom, and aerate. We used to have problems not with smell but with slime that would plug the pump intake screens. We bought something called Triadine 20 from J&L Industrial and add it according to label directions. It kills bacterial and fungus and is approved for use in machining centers. Stuff works great and now we get 6 month's out of a batch of coolant as opposed to 2 months. We could probably go longer but at 6 months I'm sure it's pretty much toast due to the high volume of aluminum we run through it. In my opinion adding a chlorine to water soluble oils that are made from petroleum products will likely produce chlorination byproducts, ie chlorinated petroleum, but then again who knows, I'm just a machinist and not a chemist:) Hope this helps.