Since I use trichlor pucks when I need to add CYA, and also get the chlorine, I have smashed up pucks with a small hand sledge hammer They pulverizes easily. Take the powder and dump it in the skimmer and the sand filter traps it and it dissolves very quickly. A few hours. You may be able to dissolve it in a bucket of warm water and do it faster yet. With a DE filter I'd try the bucket to prevent spots of high acid concentration from damaging the filter grids. Also, when you pulverize the puck place it between sheets of newspaper or plastic or something and clean off the hammer right away if any powder gets on it, or it will rust. Obviously wear protective gloves and eye protection. To repeat, I do this with my sand filter and have not heard of anyone trying it with a DE filter.
Al