Koi Pond Leaks. How to Find a Fish Pond Leak

Page Summary:  After how do I get rid of algae or blanketweed? and how do I choose a pond pump? and do I really need a biofilter? the next most common question goes along the following lines... Hello, I wonder if you can help me? My pond is leaking.... Well of course we try to help but we don't have all the answers and especially if the leak is not in the pond but somewhere in the water course, waterfall or stream section. So the tips here are to help you analyse your own leaking pond system. The first point is the following... if your pond level is decreasing at a rate at which you can notice within a day or so then the loss of water is almost certainly NOT evaporation. In other words water is leaking from the pond itself, or the enclosed pond circulating system either from the pipework connecting all the bits and pieces, losses at the waterfall or stream, or overflow from a biofilter and not necessarily in the pond itself.

Eliminate the Pond Itself.

1. Stop circulating water (ie stop the pond pump)

2. If the level of water in the pond continues to fall then the leak is in the fishpond itself and if you leave the pump switched off long enough the level will eventually stabilise at the point where the leak is. Then at least you know at which level in the fish pond the leak is occurring at. If the leak is in the bottom of the pond (eg bottom drain connection or piping problem) then the whole pond might empty so beware.

3. If the pond does want to empty itself and if you have a bottom drain then you have to suspect a leak (heaven forbid) in the bottom drain piping system. Repairs to this kind of problem are difficult to fix (maybe impossible) so if you're building a pond with a bottom drain make sure you seriously consider your pipe and access design.

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What if the pond is not leaking?

If you have a gravity biofilter make sure that the outlet is not restricted causing water to flow out the lid. By the way if you do install a gravity biofilter it's a good idea to place the biofilter in a position such that should water overflow from the lid at least it flows back into the fish pond. OK the water might get dirty but the fish will survive.


If you have a number of pipe connections and you will have probably then check for obvious tell tale signs of water leaks (wet ground, drips at connections). Points of pipe connection are always suspects in any pond water loss situation.

If you have a waterfall or stream look for obvious signs of water loss... wet ground is a classic symptom.

Construction of waterfalls is far from easy and if you have an elaborate hand-built waterfall it may well be very difficult to find any water leak since water has an amazing ability to find its way through the smallest of holes or gaps and it also has a wicking tendency. Correct use of liner to seal waterfalls is important and if you tempted to build one yourself go and find the ebst practical advice you can using the power of the Internet.

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In this article I'm providing you with some ideas to locate leaks. Treatment of leaks is another matter since repair may or may not be possible and repair depends greatly upon the material of construction, location and size of leak.

Repairing Leaking Ponds and Koi Fish Pond Systems

In theory concrete ponds can be resealed using a wide range of sealants but I've heard of more failures than success. No doubt due to the extreme care required to seal a leak in a pond environment.

PVC and other polymeric pond liners (Butyl rubber liners, EPDM synthetic rubber liners, and even polyethylene liner) can be patched. The good thing (if you can say that) for a leaking liner pond is that if you can't repair it you can replace it relatively easily and cheaply. Bradshaws supply the best priced and largest range of pond liners.

Concrete ponds that leak are best sealed using a fibreglass resin although you might want to try a propriety pond sealant first BUT follow the instructions to the letter.

Leaks in stone built waterfalls can often be plugged using specially made foam spray sealants.

Finally Good luck in trying to find your leak... the motto is when you first build a pond do it properly, take some trouble, use quality materials and especially quality fittings. Make pipework accessible or be prepared for the swearing and cursing that will inevitably happen.

Use stainless steel or plastic fittings especially if you use jubilee clips.

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