A healthy pond should be relatively bubble-free. If you have some bubbles forming on the surface of your pond, this is typically caused by a build-up of dissolved organic compounds. Several things can cause this build-up of organics in the pond.

The most common cause is overfeeding your koi. But what if that isn’t the case? The next step is to look at your filtration.

Foaming can occur in the early spring if the beneficial bacteria in your filter have not had a chance to recover from the cold winter water. Try cutting back on feeding for a while to see if the filter can catch up.

However, if it is mid-summer and you are still having issues, your filter may be too small to handle your current fish load. Consider either reducing the number of fish in your pond or moving up to a larger filter.

If suddenly over a one or two day period you get foam on the pond surface, it may be that your koi are spawning. Look carefully at the sides of the pond. If your koi have spawned, you will likely see hundreds, if not thousands, of tiny eggs attached to the pond’s sides. If this is the case, you will need to carefully check the pond’s water quality over the next two weeks.

When larger koi spawn, they release a considerable amount of organics into the pond and filter system. Most filter bacteria are not prepared to cope with this extra load. You may get a spike in ammonia and nitrite levels. It is best to clean your filter as soon as possible to remove much of this organic load. If you hope to get some new koi from this spawn, you will likely have enough eggs in the pond to have some survivors. If you don’t clean your filter, please be mindful that your water quality may degrade to the point of endangering all of your koi.

Want clear water all the time? Your filter may not be up to the task! Consider upgrading your filter system. You may also need water treatments!