There are a several factors that will impact the life of your cleaner baths.
The first is the condition of parts being placed into the bath. If they are covered in and dripping with oil and grime, your cleaner is not going to last very long as it will have a lot to clean up. This is easily fixed by lowering the amount of oil used to ship or manufacture the parts.
The second factor that greatly affects cleaner bath life is the quality of the water being used to make up the bath. There are three broad categories of water, and each has different properties that may influence the bath life. The types of water are hard, soft, and purified.
Another element that will affect the life of a cleaner bath is the type of cleaner used. There are many types of oils and compounds used to manufacture parts, and for every oil and buffing compound, there is a surfactant/soap that will clean it.