Those filtertechnik towers were originally designed to be used at very high pressure. The crude bio was mixed with magnesol then passed through the tower. As the filter element got caked with magnesol it served as a filter to remove the rest of the magnesol fines.
There is only one other person in the country that still uses magnesol besides myself as far as I know. I love the stuff but you have to be careful with it.
Nige, you can use the tower with just normal media in it but if I were you I would carry on water washing.