I added, against my original intention, duckweed this weekend past. I did not want a small floater that would be uncontrollable on the surface as I am running LED lighting and didn't want more shade on the bright side of the tank. I felt I needed a floating plant due to an addition of nine "hefty" fish on the weekend in order to help with the added ammonia production... my LFS only has duckweed. Fine, I succumbed as my fish's health is important.
I realized right away that I needed to physically segregate the surface of the water. The tank has a cross bar support which I usually bring the water level very near to, it's my level guide when filling. The bar is a "T" shape to the top is horizontal and the bottom extends down a bit. Easy fix was to raise the water level up to submerge the bottom of the "T". Downside, I can't put my arm in the tank without overflowing the tank. Not a great long term fix.
See pic one, it worked like a charm.
...Until the next morning when my daughter asks me if I put the duckweed on the other side?
Somehow the duckweed had moved over to the other side, about half and half. Watching it for a few minutes I couldn't see how it was getting over so I scooped it back again. I have since done this four times now... not something that I want to keep doing.
Today I wake to find that 80 - 90% of it is ALL ON THE WRONG SIDE!!!
Obviously it is getting jostled enough by the filter output to push it over, I noticed a slight gap at each end of the "T" bar and that is just large enough for the weed to scoot through,a few every once in a while. It all adds up.
So, I am going to do two things, I want to reduce the current in the tank so I will make a tube diffuser but I still want to reduce the water level a bit so I am also going to come up with another method of corralling the duckweed.
Option 1) a deeper T assembly.
Option 2) a rigid loop fixed to one area in the tank
Because the surface of the water is not really visible I don't mind having something else there for this purpose. I am tending toward the loop idea.