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What’s Causing the White Foam in My Koi Pond?

Cause of White Foam in Koi Ponds San Diego, CA

Many koi pond keepers strive to keep their water looking crystal-clear at all times, but this isn’t always possible for various reasons. Any garden pond that gets at least a couple of hours of sunlight each day is bound to go through periods when algae will bloom. Depending on the algae species, this natural process can give the water an unsightly brown or green color. Terrestrial plant debris that decomposes at the bottom of the pond can result in tea-colored water. Then you have the issue of excessive foaming on the surface, which can be explained by other reasons and is generally easy to take care of.

Spawning Koi and Goldfish

Nishikoi, shubunkin, and common goldfish are some of the favorite species of garden pond keepers. These three fish species trace their genetic lineage to Asian carp, and they share similar reproductive behavior. When these fish spawn, which they usually do when temperatures rise in late spring, the surface will appear to be oily, and foam will appear at the edges of the pond. The surface will also emanate a strong fishy odor. When this happens, it usually doesn’t last for more than a few days, but you should be ready to perform a 20 percent water change and test the water for ammonia. After a water change and the addition of fresh liquid bacteria, the pond filtration system should take care of clearing up the water.

Algae Treatment Agents

One of the essential koi pond supplies you’ll want to keep on hand is a high-quality and safe-to-use organic algae control like CrystalClear Clarity Max:


In some cases of severe algae bloom, pond keepers will have no choice but to use a bottled algae killer solution. Depending on the formulation, these water treatment agents may contain hydrogen peroxide and other compounds that result in foaming. Organic algae killer formulas, which are made with bacteria and barley straw, are more likely to cause frothiness on the surface because their organic matter will decompose quickly. As long as the water testing kit doesn’t indicate that ammonia levels are rising, this type of foaming is nothing to worry about, and it should quickly go away on its own.

Dissolved Organic Compounds

Koi food that’s high in protein is usually recommended to pond keepers who wish to maximize the growth of their aquatic pets. The byproducts of these pellets start turning into dissolved organic compounds as soon as they hit the water. Uneaten food that falls to the bottom will eventually decompose and dissolve into a froth. In this case, foamy conditions are bound to last longer, but you can avoid them altogether with frequent water changes, stocking the pond with bottom-dwelling species such as Brochis splendens or small catfish, and of course by not overfeeding your fish.

Water Quality Issues

In the absence of the situations listed above, pesky pond surface foam may be caused by water quality conditions that aren’t necessarily related to ammonia levels. Inadequate aeration and filtration systems are usually to blame in this regard because they’re not able to handle dissolved plant matter. Larger filters, stronger pumps, fountains, and waterfalls can go a long way in terms of preventing foam.

It’s important to pay close attention to what’s going on in your pond and maintain it properly with all of the essential supplies. From pond vacuums and filters to beneficial bacteria and nutritious koi food, Aquatic Warehouse has everything you need to keep your pond looking beautiful and its inhabitants happy and healthy. Stop by our store in Kearny Mesa, order what you need from our website, or give us a call with any questions at 858-467-9297.



Contact Information

  • Address: 5466 Complex Street Suite 204
    San Diego, CA 92123
  • Phone: (858) 467-9297
  • Email: sales@aquaticwarehouse.com
  • Working Days/Hours: Mon - Fri / 10:00 AM - 7:00 PM
    Saturday / 10:00 AM - 6:00 PM
    Sunday / 11:00 AM - 6:00 PM


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