A low flow rate with a hollow fiber filter like the Guardian Gravity has s few potential causes, so let’s have a look at them individually.
Dry Hollow Fibers
Just like a wet sponge absorbs water more efficiently than a dry one, the porous walls of hollow fiber filters need to be wet to effectively draw in and pass water through.
If your filter is new or has been in storage for a while, the fibers likely need to be re-wetted. The easiest way to do this is simply by using the filter. The first liter may flow slowly, but if dry fibers are the issue, you’ll notice a significant improvement in flow rate after filtering a liter or two.
Trapped Air
If you're using a wet filter and the flow still seems slow, check for air in the system. Air bubbles trapped inside the filter or clinging to the hollow fibers can block water from passing through efficiently.
To check for air, gently tap the cartridge while filtering, with the clean side of the cartridge facing downward as usual. This helps dislodge any trapped air, allowing it to escape into the dirty water reservoir. If no air bubbles appear and the flow remains slow, your filter may be clogged and in need of backflushing.
Clogged Filter
Everything your filter removes from your water stays inside the filter—unless you remove it through backflushing. Regular backflushing is the single most effective way to maintain your filter’s performance and extend its lifespan. Without frequent cleaning, the filter becomes less effective over time, reducing its ability to process water and shortening its usable life.
To learn how to properly clean and backflush your specific model, refer to your instruction manual or visit the Help Center. We also offer step-by-step instructional videos on the product page at CascadeDesigns.com.
Our instructional videos are hosted on YouTube, and you may be able to find them more quickly by searching directly there. Each brand has its own channel; Platypus, MSR Gear use the channels’ search tool located next to the Playlists button.
Poor Storage Hygiene
If none of the previous steps have improved your filter’s flow rate, mold may be the culprit. Hollow fiber filters must be sanitized before storing them for more than a week. This is easily done by running a weak bleach solution through the filter. If not properly sanitized, mold can grow inside, forming a layer over the hollow fibers that blocks water flow. Unfortunately, this damage is irreversible and will require filter replacement.
To learn how to properly sanitize your filter, please refer to the instruction manual.