It's probably a shortage of traces or something similar. I use a mixture of substrate and liquid fertilizers and when I see the cuba or stellata doing this I know it's time to add more tabs to the substrate. So far it has worked well for me. Don't know about the pantanal, you'd have to send me some to try ;-) (hint hint.....)
Hope that helps
Giancarlo Podio
Hope that helps
Giancarlo Podio