I think the nests all depend on the betta itself. Arakasi, my other betta, would build a bit of a nest when I first changed his water, but it would fall apart after a few days. Kabuki builds these huge nests that don't go away until I change the water and then he goes right back to building. That little green juvinile I had posted a pic of in an earlier thread never really did get around to any nest building, and then he died.
Question: Has anyone else ever had a problem with blood worms and fin rot? It seems every time I try and feed those worms, I spend the next two weeks battling rot...so I quit feeding the blood worms and no rot in sight.