A low flow rate with a hollow fiber filter like the Guardian Gravity or QuickDraw has a 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 pages at CascadeDesigns.com.
Tea-Colored (Tannic) Water
This color of water typically comes from a high concentration of decaying vegetation adjacent to, or in, streams and lakes, resulting in a variety of organic acids. These include, but are not limited to, tannic, fulvic, and humic acids. These acids and the accompanying water conditions are very hard on ALL types of water filters.
Get your water elsewhere if you can. However, if no alternative exists and you are predominantly filtering these waters, we recommend using an MSR® MiniWorks® EX filter. Its ceramic element will collect all these impurities in its outer-most layer, allowing you to scrub away the clogged portion to restore normal flow rates. If you must use a HyperFlow filter, backflushing frequently will help to minimize the effect of these impurities. When you return home, add 2 drops of unscented household bleach to one liter of water and backflush this solution through the filter. This will help to break up organics that might be clogging the filter and provide the recommended treatment of your system for long-term storage.
Limited use in these conditions will not have a dramatic effect, but extended use can permanently impair hollow fiber media.
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.
Long Term Storage (more than a week or so):
Run a solution of a 1/2 tsp of bleach per 1 liter of water in the filter and store it as-is. This will need to be stored above freezing to protect the fibers but it should prevent them from closing up as well as prevent any mold growth. This is how the Guardian purifier is stored; many folks have adopted it for all Hollow Fiber filters. Store the filter in a plastic bag to ensure it keeps wet and does not stain any other gear, flush a few liters of fresh water before the next outing.
Can I tell if I’ve damaged the hollow fibers?
Yes, you can, but sometimes not just by looking at the Filter Cartridge. If you have experienced a hard drop or may be concerned that your pump has frozen, there is a Filter Test Guide that came with your system. This includes instructions for checking the integrity of your filter. Also, please view this informational video about checking filter integrity. Essentially you’ll be intentionally air-locking your filter to prove the integrity of the hollow fibers. In preparation you need to make sure that your filter is fully wetted out. This means that you should have pumped several liters of water before performing this test. Generally your filter cartridge will not dry much during storage, so as long as you have used the pump a few times, you should be in good shape.
What happens if my filter cartridge freezes?
Once you have used your HyperFlow and wet the Hollow Fiber filter media, the fibers will remain wet for a very long time. Therefore, it is important to prevent it from freezing which can permanently damage the filter media. If you are traveling in areas where you are expecting freezing or near freezing temperatures, bring the filter into your tent - or even your sleeping bag if freezing is a definite concern. The Cleanside cover is watertight and will prevent any leakage wherever you store it. If you think your filter may be damaged from freezing, perform an Integrity Test before the next use.
What if the filter takes a hard drop?
The casing of the pump is designed to protect the Filter Cartridge from most drops, but direct drops onto cement (or similarly hard surfaces) and any drops above 4 feet (1.2 m) should be avoided. If a Filter Cartridge outside the pump housing is ever dropped after being wetted, you should replace the Filter Cartridge. (We don’t recommend removing the Filter Cartridge from the protective pump housing except to replace the Filter Cartridge.) If you think your filter may have been damaged from a drop, perform an Integrity Test before the next use.
Replacement Filter Cartridges
- DayCap Replacement Filter Cartridge
- Gravity Works Replacement Filter Cartridge
- AutoFlow Replacement Filter Cartridge
- QuickDraw Replacement Filter
- Guardian Gravity Purifier Replacement Cartridge
- Guardian Purifier Pump Replacement Cartridge
- MiniWorks / WaterWorks Ceramic Element
- TrailShot / Trail Base Filter Cartridge
- HyperFlow Microfilter Replacement Cartridge
To learn how to properly sanitize your filter, please refer to the instruction manual.