Vals will often melt on move from one tank to another, then return later once they have acclimated. I found mine did much better with root tabs than not, even with good water column ferts. I have heard they do not do well with excel (liquid co2) but mine do, I add about 1ml/10g daily. To be safe if you decide to use it, maybe ease into it with them, adding at first half as much and work up.
They spread by runners in a straight line; to help this, wait for the new shoot to be a few inches tall, cut the runner (it stays a long time) and then transplant as you would otherwise. They tend to make a mess when they run into glass as they do not reroute this straight line gracefully, so help in their spread is useful.
I trim mine when they get too long (I've had them over 6'), they seem to spread a bit more if you trim more aggressively, but emphasis on "seem".
I find they look best when they are growing under a water stream flowing past, lengthwise in a tank, so they have room to spread out. If the stream is blowing toward them, as the leaves get long they make a tangled mess (though, some people might like that).
I have them growing equally well in sand and in gravel.
My experience is with the Americanus (jungle) val variant, there are others and I know naught for those.
