It's added at a constant rate to the liquid entering the filter, so it builds up at a constant rate. However, this can be varied depending upon the filter back

It's added at a constant rate to the liquid entering the filter, so it builds up at a constant rate. However, this can be varied depending upon the filter backpressure. If the particulate load is high, you need to dose at a higher rate or else the filter will start to blind. In practice this is based upon manual calculation and adjustment. In the place I worked, the filter room had two of these, each about 1.5 storeys high. It had a dedicated control room to operate, and the two operators would be continuously monitoring and adjusting the flow rates, dosing and other parameters to ensure efficient operation. When you have an unexpectedly dirty product or you muck up the calculations, the flow rates can become very low and that starts to cost serious amounts of money when it's a rate-limiting step in an industrial process. When the filter becomes too inefficient, the backpressure excessively high, or the filter depth approaches the tank capacity, the metal filter plate is spun and this destroys the filter bed which is spun off. The coarse filter base is then reapplied to "regenerate" the filter.