Hi all, reading along in this forum quite some time. This is an interesting thread. Duckweed is not my thing. Tried Limnobium more than 20 years ago, but never survived. Back than I believed NO3 and PO4 was root of all algae bloom I had in my tank. Until in 2008 the approach of Estimative Index came into my life. That was a major shift in thinking about nutrients, and my plants loved that. Nowadays I use Salvinia to check whether Fe and trace are needed in a small more neglected tank. Does new leaves gets yellow (and overall growth is poorer)? If so, then dose FE-traces-mix more often.
But checking how green the leaves are as indicator never arose as an idea, maybe ample macro dosing in tap water never gave issues nutrients wise.
But still, Limnobium still is one of the plants I like to try sometimes, and seems a good indicator somethings off. I just got the amazon frogbit in, as well as
Phyllanthus fluitans to give that a go as well.
Okay, so let me try to recap.
Lymnobium as a floater gets it's carbon from the air, and can be used as good indicator plant for the water column nutrients.
If it doesn't maintain a ' darker' greenish look (like some healthy photo's in this thread), nutrient dosing like N, K, P and/or Mg dosing may do the trick.
When new growth is pale and yellowish, a non mobile nutrient dosing can help. Such as S, Ca, Fe, Mn and other traces like Ni, Cu, Zn and B.
For fixing things, it's up to the aquarist to determine whether going for full scale dosing (for instance Estimative Index dry dosing of using an all in one fertilizer), or start checking them individually. It takes time for a plant to recover, so maintaining higher nutrient levels seems logical.
@dw1305 Darrel, Am I way off in this recap?