Pond Filter Not Working? 7 Things to Check | Aqua Pond
A pond filter that has stopped working usually shows itself in one of two ways: the water turns green or murky, or the flow from your waterfall or fountain drops away. Either way, it is worth acting quickly, because your fish rely on the filter to keep the water clean and safe.
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Pond Filter Not Working?
The good news is that many filter problems have a simple cause. Here are seven things to check, in the order we would check them ourselves. If you get through the list and the problem is still there, we are happy to help.
Safety first: always switch off and unplug the power before touching a pump, UV unit or filter. Never handle pond electrics with wet hands, and never open a UV clarifier while it is plugged in.
Is the power actually on?
It sounds obvious, but it is the most common cause. Check that the plug is in, the socket is switched on, and that your outdoor RCD (the trip switch) has not tripped. A tripped RCD after rain or a storm is very common. If it trips again as soon as you reset it, leave it off: that points to an electrical fault that needs a professional.
Is the pump intake blocked?
Leaves, blanket weed and silt build up around the pump and its pre-filter. If the pump is working but the flow is weak, switch it off, lift it out and clear anything blocking the intake. A pump starved of water can overheat, so do not leave it running blocked.
Is the impeller clogged or worn?
The impeller is the small spinning part inside the pump. Debris, algae or a build-up of limescale can slow it or jam it completely. If the pump hums but does not move water, or sounds rough and noisy, the impeller is the usual suspect. Cleaning it often fixes the problem. If it is cracked or worn, the pump may need replacing. Pumps are the most common part to fail in a pond, so this is a frequent repair for us.
Is the filter full of waste?
A filter packed with sludge cannot do its job, and water will struggle to pass through it. Signs include a weak return flow, a smell from the filter box, and water that stays cloudy. Clean the media when needed, but rinse it gently in a bucket of pond water, not tap water. Chlorine in tap water can kill the beneficial bacteria that break down fish waste, which means your filter stops working biologically even though it looks clean.
Are the pipes and hoses kinked or blocked?
Follow the pipework from the pump to the filter and back to the pond. Look for kinks, loose connections, collapsed hose or a blockage. A small air leak on the suction side can also cause poor flow and a pump that sounds like it is gurgling.
Is your UV clarifier doing its job?
If your problem is green water rather than poor flow, the UV clarifier may be the cause. UV bulbs lose strength over time and generally need changing about once a year, even if the light still comes on. The quartz sleeve around the bulb also needs cleaning, because a dirty sleeve blocks the light. Remember that a UV only clears free-floating algae. It does not replace a healthy filter.
Is the filter big enough for your pond?
If everything works but the water never really clears, the system might simply be too small. Ponds change over time. Fish grow and multiply, trees get bigger, and a filter that was fine five years ago may now be struggling. As a rough guide, if your filter is more than 8 to 10 years old, or you have added fish since it was fitted, it is worth getting it assessed.
When to call a professional
It is time to get help if:
- The pump will not start, trips the power, or makes a grinding noise
- You have checked the basics and the water is still green, cloudy or smelly
- Your fish are gasping at the surface or hanging near the water outlet
- The filter is old, undersized, or you are not sure what is wrong
Fish in trouble is the one to act on fast. Low oxygen or a build-up of ammonia can harm them quickly, so do not wait.
How we can help
We clean, repair and replace pond filters and pumps across Bedfordshire, Hertfordshire and Buckinghamshire. We carry replacement pumps in our vehicles, so many faults are fixed in a single visit, and we always tell you plainly what is wrong before you decide anything. If your filter has had its day, we can size and install a new Oase filtration system for your pond.
Read more about our pond filtration systems: cleaning, repair and installation, or find out how regular pond maintenance keeps filters and pumps running well. Prefer a full reset? See our pond cleaning service.
Not sure what’s wrong? Send us a few photos and a description of the problem on 01525 552150 or via our contact page, and we will tell you what we think is going on.
Frequently asked questions
Why is my pond filter running but the water is still green?
Green water is usually free-floating algae. A filter alone often cannot remove it, so a working UV clarifier (with a fresh bulb and clean sleeve) is normally needed. Too many fish for the pond size, or too much sunlight, can also be factors.
How often should I clean my pond filter?
It depends on fish numbers, overhanging trees and the type of filter. Ponds with lots of fish or trees need cleaning more often, especially in the growing season from March to November.
Can I fix a pond pump myself?
Cleaning the intake and impeller is a job many pond owners can do, with the power off. Anything electrical, such as a damaged cable or a pump that trips the RCD, should be left to a professional.
How long do pond filters and pumps last?
It varies by quality, how hard the equipment works and how well it is maintained. Regular servicing extends the life of both. If your equipment is more than 8 to 10 years old and struggling, a replacement is often better value than repeated repairs.