Vallisneria "mystery"

Hi, and I hope this is the appropriate section for this post.

I have a 75G tank that I set up, cycled, and planted in February. I am currently having a strange problem with my Vallisneria which had mostly grown up to the surface of the water. Yesterday I noticed when I got home from work that there were 6 -7 2" - 4" Val tips caught up in with my floating plants. The floating pieces almost looked like they had been clipped off, at least in that there was no sign of decay or bruising that I could really see.

I can only think of two possibilities. One is that I have been dosing with NilocG Enhance Liquid Carbon Supplement and there is a warning on the bottle to go slowly with it at first because it may adversely effect Vals. The other is my 4 x 1.2" to 2" festivums. I have been using the Enhance, along with DIY CO2, for several weeks and I don't dose every day. If it were the Enhance, does anyone know what would happen exactly to the Vals? It seems weird that just the tips would come off. Oh, and I should mention that the Vals have already recovered from their melting stage.

As for the festivums, we have seen them yanking my floating Salvinia and dwarf water lettuce under water and letting them go again, but I haven't witnessed them going after any of my other plants. Also, most of them like to hide in the tall plants when they are not eating. I should also mention that someone is yanking chunks out of my merimo moss balls because I'm finding pieces all over the tank. I know that cichlids are not really considered plant friendly for the most part, but has anyone heard of festivums acting this way?

Other tank inhabitants are really small juvenile angels, silvertip tetras, 1" baby BN, and juvenile Bolivina Rams. I'm pretty sure it was not any of these other fish. Any other explanation for the ends few inches of Vals coming off?

Thank you very much for any ideas!