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Duck Weed eradication

Consistent and prolonged manual removal is the only way. Scoop up all your existing floating plants, and get rid of the lot - possibly saving a small number of plants that are rinsed and visibly clear of any duck weed for adding back to the tank for future propagation. Then ensure every visible trace of duckweed is removed - this will require some decent tweezers.

Then it's just a matter of keeping on top of any more duckweed that appears, immediately removing it with tweezers.

I managed to remove all visible signs from one tank, and was free of it from about a month, and a month later the surface was covered with it again because I didn't keep on top of the removal of bits that appeared later on.

In a later tank, I did keep on top of the removal, but it must have taken about a month of regular (daily or bi-daily) checking and removing odd tiny plantlet that appeared.
IF you don't have any plants that penetrates the surface it's fairly easy to remove duckweed with a net - make sure you clean the inside of the tank between the rim and the waterline as well. If you have other floating plants such as frogbit, you should remove those first and rinse them in a bucket of tank water and put them in another bucket. When all floating plants are removed net as much of the duckweed as you can and attack the residual with a tweezer - its really super tedious but doable ... (it helped me to quietly curse Darrel :lol:) ... Rinse off the floating plants you removed and put them back in the tank - apply the tweezer again... This approach worked for me in one of my tanks. I haven't had time to apply the approach to my other tank where the duckweed seems to propagate slower and is less of a nuisance.

This used to be the situation every couple of weeks:

Now I only have to grab a couple of fistfuls of Frogbit every two weeks or so.

Has anyone tried spraying the hydrogen peroxide on the surface? I honestly haven't tried this yet but I believe this will get rid of it.
Tropheus love the stuff
Not an ideal addition for most plant orientated aquarists though
I have some videos (which I will look for), which show a tank of Ikola and a tank of illangi, with some large cryptocoryne aponogetifolia, these plants can survive as long as the fish are well fed, I have subsequently kept various wendtii with tropheus, and found that they helped with breeding. The females frequently released the fry into the plants
I found the biggest issue was keeping the plants “planted”, at least initially, as the fish pulled them up, I “planted” the cryptocoryne aponogetifolia in ceramic flower pots, after a while the crypts would send out runners and thus spread out, once they were established, they did ok
It's a bit tedious but works ,Every time you do a water change,at least weekly more if you can take as much duckweed from the surface,in my case it was mixed with, Salvinia, so l just tried to put some Salvinia after the W/C back in. After a couple of weeks was rid. and left with just Salvinia
I've recently managed to get rid of it by first removing as much as I could manually.
I have lots of plants, floating plants and branches above the waterline so couldn't get all of it. Then I stopped dosing ferts, continued doing 50% water changes with rainwater and eventually the salvinia managed to out compete it.
I do feed heavily and my tank is not a beautifully aquascaped tank so less than optimal plant growth isn't unusual and hasn't really changed even with the total lack of dosing.
Another approach is to essentially drown it as shown here.