String algae in waterfall--becoming a nuisance.

[hobie61]

Hi,

Seeking advice for limiting hair (string) algae growth.

I have an approx. 2500 gal pond (with a lined rock waterfall) which i keep koi. Live in northern VT, so summers are relative short. It has been hotter than normal (?) this past summer. Probably not quite a couple dozen koi in there with various sizes. All seem healthy. Feed once a day. Its been going for almost 25 yrs. I do upgrades every now and then. Running an upflow filter, Aquadyne koi filter, and bog filter. Air pump. Larger main pump this summer, so good flow. Rinse the main filter once a week. Always had problems with green algae in the water, so added a 40w UV light this spring (from various recommendations). Water has remained absolutely clear all summer, so that worked well. I now am dealing with lots of string algae in the waterfall till the point it is being a big nuisance. At least once a week cleaning by hand. I cant remember ever having such a nuisance/problem. I realize its a nutrient/poop issue. I treat with bacteria and yeast. Add some salt once in a while. Any recommendations for helping to control the algae growth in the waterfall? Doesn't seem to be any string algae in the pond area itself. don't like to use chemicals. Probably have another month of the algae growth before colder temperatures set in.

Thanks much for your time to review and guidance.

 

[Mmathis]

Basically, any time there is algae, it’s because there are excess nutrients in the water. The first thing I think of is that maybe your biofilter isn’t able to keep up with waste products. Plants are a great way to soak up those extra nutrients, but if you don’t have plants, guess what…..algae equals plants, so Mother Nature adds her version of plants to compensate.

The next thing I think of is an overstocked pond. Koi produce a lot of waste. You say your pond is 2500 gallons and you keep koi. How many koi? That size pond is good for maybe 2 or 3 koi. Over feeding can contribute, as well…..anything that can lead to excess nutrients in the water. Keep in mind that over time, those koi have been growing. Bigger fish produce more waste.

Something like a toilet bowl brush is good for removing string algae, but to keep it away, you need to address the cause of the algae. (I’m dealing with this right now — my problem is a slow leak that is reducing the water volume, which is concentrating the waste products. I have goldfish, though. Going to be dealing with it this weekend by fixing the leak and getting my water volume back up)

 

[Lisak1]

@Mmathis nailed it - your pond is overstocked. You are fighting a losing battle. You need to reduce your bio load or you will constantly fight algae. And worse than that you’ll eventually start to lose fish.

UV light does nothing for string algae. It will kill single cell, floating algae, but it will also kill all single celled organisms that pass by the light. All algae has the same cause in a pond – excess nutrients. Until you change that situation, you will continually battle algae of all types.