Yup they're easy to build but the plastic canvas is not the right material for any submerged scrubber, IMO. Algae doesn't seem to strongly attached to that material when submerged, the glued-on quartz version works better. Also worth a note, he got his UAS patent.
Do you have any info on how to attach the quartz to the plastic case? I have heard 2 part epoxy spread over it with quartz sprinkled onto the epoxy can work but I have not seen any that have done this.