I asked because some plants like Corkscrew Vallisneria can work in small tanks but they are best in harder water than others. In softer water, the chain swords are ideal. I have these in most of my tanks; they will grow somewhere between 3 and 5 or sometimes 6-7 inches tall, and once established, send out runners everywhere. You can leave the plantlets to spread, or cut them off.
Some species of crypts work well in smaller tanks but they can be fussy about water and just about anything, melting. Floating plants always work, and corys and tetras do not appreciate overhead light so this is good for them too.
Generally, stem plants do not work so well in small tanks because they grow so fast you will always be trimming them, removing the planted ends and planting the cut growing ends. Some do make good floating plants though, like Pennywort.
The common Amazon Sword does get large, but in smaller tanks it can take quite a while to do this. My larger plants in thee big tanks send out inflorescences with adventitious plants regularly, and sometimes I will remove these and plant them in my smaller tanks, even a 20g. I have had these remain smaller for years. One as a specimen plant can be very effective.
I'm attaching a photo of my Quarantine Tank as it was a couple months back; there are two of these amazon swords, and some of the chain swords that will illustrate what I've been saying. Getting some Java Moss growing on wood is also a good idea, both visually and for the fish.
