Koi Fish

Without a doubt, koi pond algae are most certainly the biggest thorn in the side of koi fish keepers… not only because of the ugly appearance and odor it creates… but because of a more harmful reason – algae threatens the very lives of their fish if not stamped out fast!

And yet the truth is you can prevent algae amassing quite quickly and get around the problem… controlling algae is easy if you understand the best way to go about it!

Koi Fish
Koi Carps Fish

And on that note, here are some valuable tips that will quickly aid you in getting koi pond algae under control.

There are two main ways to control algae – with chemicals or by natural means.

This article discusses natural means. We will review chemical algae control in later articles.

It must be said that natural management is preferable because it won’t interfere with or cause any imbalance to a pond’s ecology. That said, there will be occasions where you will have to use chemicals, which is acceptable because it is not the solitary type of algae treatment.

So first, let’s look at the key reason koi pond algae is life-threatening, and from there, we will look at prevention.

The main reason is that rotting algae produces ammonia, and excessive ammonia will soon diminish the oxygen supply… and needless to say, koi fish without oxygen are identical to humans with no air… they start getting sick, and ultimately they die!

Koi Fish
Japanese Koi Fish in the Pond

But do not panic – here’s some good news… with some careful planning, you will be able to deter algae from growing, stop harmful hazardous ammonia buildup, and remove your koi from risk.

Therefore to curb it, here is what algae require to live – sunlight and the proper nutrients. If you limit these two things, you severely curb its growth or even eradicate it, which is why you need to plan wisely.

Restrict the amount of direct sunlight on your koi pond

Sunlight and Koi Fish
Koi Fish in the Pond

This isn’t implying that sunlight on your pond is terrible because it does need some, but you need to consider how to avoid having sunlight off the bottom of the pond as you can because that’s the fortress of algae growth.

So if you are building a new koi pond, consider making as many sections as you can, at least four feet deep… if you go deeper, fine, because sunlight struggles to get beyond this depth.

Of course, you will still want some shallow sectors around 18-24 inches deep, so in these regions, consider deploying the use of plants with plenty of big leaves to form plentiful amounts of shade.

Water lilies produce great shade with their broad leaves, not to mention that they look nice and enhance your pond’s appearance.

For folks with an existing pond that cannot be changed as far as depth goes, it will be beneficial to consider planting lilies and building some overhead shade. Something like a timber-framed shelter with shading cloth fixed over the top… you have many alternatives, and a little imagination will go a long way here… but you get the idea, right?

If you can get 70-80% under shade… you’ll be amazed at how rapidly the koi pond algae growth slows down.

Get rid of the nutrients that help algae grow

Koi Fish

Just as important as limiting the amount of sunlight is eliminating the nutrients that algae need to live… take away its nutrient source and starve it out!

Remove all things like:

  • Fish waste
  • Rotten fish food
  • Dead and rotting algae
  • Dead or dying fish (yes, they do die on occasion)
  • Rotting leaves and debris
  • Particular phosphates and tap water nitrates

It does involve frequent cleaning and skimming your pond, as well as a good pump and filtration system to circulate the water, but the advantages far outweigh the small amount of extra work. As referred to above, you will literally be starving the koi pond algae to death!

Not to mention… a good clean pond reveals the care you have for your koi.

So use these two simple tips, and you’ll be pleasantly surprised how quickly plankton algae starts to become less of a problem – allowing you to get on with the real fun stuff – like enjoying your healthy koi!