Benthic PBR geometries compared. Phormidium autumnale (CAWBG26) was grown in the bags as described in the Materials and Methods section. panel a, horizontal PBR bags; panel b, vertical PBR bags; panel c, silicone tubing added in a coiled spiral (using a flexible wire inserted within to shape); panel d, a PVC bottle brush inserted into the PBR; panel e, 'looped silicone' where silicone tubing was folded back upon itself several times and pinched together at the bottom using a silicone tie. These loops were able to move about in the air bubble stream. Dimensions shown on the insert for panel b are the same for the other geometries.