Water lettuce (Pistia)

[freesia]

I put water lettuce one month ago in to my tank. It was growing beautiful for month and suddenly the roots started to fall off and some parts of them turned into a brown color. What is the reason?
Tank is 10 gallon with betta only
Photoperiod 10 hours
Lights: two fluorescent bulbs 10W each 5100K each
Sponge filter
Temp. 79F
Other plants: sword and anubia are OK
Thank you,

[Aus]

Mine did the same. I don't think it liked its roots being in the substrate, or the lower levels of the stems weren't getting sufficient light. I broke off the rotty bits and left it floating, which my betta just loves. The plant has recovered beautifully, with new leaves and lots of dangly roots off the stems - so I'd say it's maybe a matter of it needing good light on its stem as well as on the upper leaves.

[LittleBettaFish]

I think water lettuce does best in a pond situation. I had some and was running high-light and dosing daily with iron and other ferts and mine still died off.

It's a shame as we can't seem to get the smaller water lettuce or other plants such as giant duckweed or red root floater here in Australia.

[Aus]

Oh bleh - my bad, replying half awake.. I was talking about the wrong plant.

[freesia]

I bought Nutrafin Plant Gro, maybe watter lettuce need some nutrition... My Betta sleeps in pistias's roots, so I really want to have it in his tank. Any suggestion? please..