Hanne, it is probably a type of Filamentous Algae and nothing to be too concerned about.
There are thousands of types of Filamentous algae, with common names such as Blanket Weed, String Algae, Angel hair Algae and on and on.
You may have added a new common name, with your "Hairnet Algae" LOL.
See the link below for a little bit more information.
Hope you are having a good summer in Denmark!
"Horton"

Here is a link that might be useful: Filamentous Algae.

It is probably contributing to your clear water. You can use a brush to twirl some of it out if it is bothering you.

Thanks to both of you for your replies.

I have actually used a toilet brush (bought new for the purpose :-D) once to pull it out.

But Im definately not pulling anymore if it clears my water. It doesnt bother me, as its a pretty healthy green, and it stays partly hidden around the waterplants.

I dont know if you can see it in these pictures, but it is so hair net like :-D

{{gwi:222463}}

{{gwi:222464}}

I must admit that I have been anciously waiting for my water to go green or brown, as Ive read it mostly do at the beginning of a new pond, but it hasnt yet. So maybe I was really lucky to get a bunch of these with my first plants.

Another question though... will the goldies (blushing, see other post) eat this algae? I definately seem to have less since they moved in.

Thanks again to you both. And no, sadly summer hasnt been too good the last few weeks in Denmark. DH hols are over on monday though, then I bet the nice weather will return.

Take care,
Hanne in Denmark

Hanne, the algae does not look bad at all, I don't think you will have anything to be concerned about. Usually if the water is cool the filamentous algae will thrive and the water becomes even clearer.
If it starts to take over just scoop it out, or you can pour some Hydrogen Peroxide [3% strength] over it and the HP will kill it. After it turns brown scoop it out.

The goldfish will nibble away at it, especially if you do not feed them commercial fish food, that will help keep it under control.
Take care and enjoy your pond.
"Horton"

Thanks for all your help, Horton.

I didnt feed the goldies much the first few days, cuz they were too scared to come to the surface anyway. And they seemed really busy eating all the stuff that had already built up in the pond.

But now Im making sure that they get a bit of food too, cuz I definately dont want them to eat my hair net algeas. They have already cleaned the pond completely out of bits and bugs.

I hope youre having a nice summer too.

Take care,
Hanne