Filamentous algae in the stream is persistent

[myswtsins]

Hi.

Water quality
* Ammonia Level (pond) 0.0
* Nitrite Level (pond) 0.0 nitrate 0.0 also
* Ammonia Level (tap water) 0.0
* Nitrite Level (tap water) 0.0
* Ph Level, pond (If possible, KH, GH and chlorine) ph 8.2, kh 6, gh 3, phosphates 0
* Ph Level, tap water (If possible, KH, GH and chlorine) 7.8, 6, 4, 0
* Brand of test-kit used and whether strips or drops? API liquid test

Other useful information:
* Water temperature? 83F
* Pond size and how long has it been running? ~4,000g, running since the end of the summer last year
* What is the name and size of the filter(s)? 10'x3' gravel bog, 30ft stream, lots of plants
* How often do you change the water and how much? 50% water changes in spring and fall during cleanout but besides that water is removed when it overflows (often enough) and is replaced by rain or auto top off (auto top off rarely comes on)
* How many days ago was the last water change and how much did you change? see above
* How many fish in the pond and their type? about 20 standard goldfish ranging from 4in to 12in
* What kind of water additives or conditioners have you used? none, well water
* What do you feed your fish and how often? drs foster and smith staple, every other day and are feed very slowly so no food is allowed to escape the fishes mouths (none goes into the skimmer or around the edge)
* Any new fish added to the pond recently? not since last fall
* Any medications added to the pond? never
* List entire medication/treatment history for fish and pond. none
* Any unusual findings on the fish? one fish as had a popped eye for a month now, seemed caused by some sort of trauma while they were breeding
* Any unusual behavior like staying at the bottom, not eating, etc.? no

So, I had green water this spring which was expected being it's first spring, that passed naturally. But this filamentous algae in my stream is stubborn. It is only in the stream. It may be several types of filamentous algae, some is tough and coarse, some in slimy, some is bubbly. I have removed it several times and it just comes right back. Most of my plants started suffering just before the algae showed up (due to lack of nutrients i concluded but research indicated to just let them find their balance being that it is a new pond). When the filamentous algae 1st started i had the nice fuzzy green algae on the pond walls now it is all gone indicating it is messing up the balance even further. Besides manual removal, nutrient control or UV install (which I do not want to do) what other actions can I take?

This is the small stream after the negative edge skimmer (opposite side of the pond, much more sun here)

 

[MitchM]

You may have a buildup of detritus in between the submerged rocks, so as that detritus breaks down, it is releasing nutrients for the algae, including phosphorus that the algae is feeding off of.
The algae is using the phosphorus as it becomes available so your phosphate kit will read zero.
Every time you feed your fish you are adding more phosphorous, so you need a way to export that same phosphorous.
Harvesting plant growth (including algae) or having a mechanical method of trapping detritus and disposing of it are a couple of ways of doing that.
Your pond water is warm, so you will also see increased biological activity which will lead to faster breakdown of the detritus.
Thanks for providing answers to the above questionaire.

 

[MitchM]

Also, you have a big enough pond. I would completely stop feeding your goldfish.
There should be enough natural food for them to eat.

 

[sissy]

I sometimes wonder if my mixing koi clay in my fish food and adding it to the pond makes a big difference .I have yet to see that in my pond ,but do see it in my lily pond and it has no fish and only tadpoles but i do put miracle grow in there and I guess it loves being fed that .Waterfall pond only gets the brown muck on the rocks that the snails seem to love

 

[mgmine]

A UV light will not do any good on the string algae only the green water. I went through the same problem a few weeks ago and can tell you that it is only going to get worse.Mine started last year and even though appeared that it died during the winter it came back with a vengeance. After doing a lot of research I ended up using sodium percarbonate and it worked perfectly.. I may have made more work than was necessary as lisak1 pointed out but none the less it's completely cleared up. Here is a link to the thread.

https://www.gardenpondforum.com/threads/using-sodium-percarbonate-to-fight-string-algae.17537/