Alternathera reineckii question...

I have little stemlets of my Reineckii floating around all the time. Growth is pretty modest IMO compared to having it planted. It's especially modest when the initial plant mass is very small (since plant growth is probably closer to exponential growth).

Another alternative in your case would be to trip the apical bud and the last two stunted/deformed leaves and plant it as is... The plant will just grow more axillary buds and grow laterally (and probably give rise to more future shoots/trimmings).

Based on my experience of growing "floating" stem plants, one of the most important factors is making sure it's upright even while floating... I usually accomplish this by using a plant weight and/or tying it down with a piece of string.

If you use the above method, it prevents accumulation of detritus/debris on the leaves which can lead to BGA/other algae colonization, etc. since you can allow for some water flow.

i got some of this in the gel packs are petsmart and when it gets to tall i just snip it off and stick it back in the substrate and it does fine. you can prob float it to get new roots but i have found you really dont have to. i have it in several substrates. i stuck it in gravel from the gel packs and have trimmed several times. the trimmings i have stuck back in gravel, sand, amazonia, and mgo with sand cap. all i did was snip and put back in substrate and all is well.

as for the red all mine has stayed red but then again they get pretty good light since they are in small tanks. the bit in my moms 29 is not so red more of a pinkish tone. but the tank its self came with a cheap led when she got the tank kit and that is what is in that tank. when mine comes back (put in a new tank and ammo melted most of the leaves off) ill let you know how a single T5 goes. right now i have just 1 small set of top leaves left but the stems are still pretty red and have not melted