Different aquarium situations can need different treatments, so different Oase cartridges give you options that will fit your exact situation.
These cartridges fit BioStyle 20, 30, or 50; they also fit BioStyle Thermo 30 or 50
Fits into the BioStyle filter chamber, in place of the 30ppi filter foam
Customizable Cartridge Oase Customizable Cartridges allow you to optimize your filtration by adding up to 120mL of dry media to an empty cartridge. Add your choice of dry, solid filter media (sold separately), depending on the needs of your specific setup. Timing to replace the media depends on which type of media used, aquarium size, number of fish and plants, and filter performance. Inner capacity is 120mL, with dimensions of 0.55" x 2.3" x 5.8"
Phosphate Binder Cartridge Oase Phosphate Binder Cartridges are strong, fast-acting buffers that help limit algae growth by binding phosphates so that they cannot return to the water column. This highly porous bead-shaped media is colorless and will not cloud the water. Replace every 2-6 weeks.
Activated Carbon Cartridge Oase Activated Carbon Cartridges remove heavy metals and other toxins; odors; tannins, cloudy water, and colors. The small, low-volume pores on this carbon make the absorption very effective. Replace every 3-4 weeks.