Yes, those are hyacinths. They can overwhelm the water and reduce oxygen levels, but 6 in a pond won't cause a problem--I've had more than that in tubs.
Food might have been a problem--could have had a bacterial growth, or started to decay, and the smaller fish didn't eat enough? That's a very protein heavy diet--I'd add some veg. I know the fish will eat it, but barbs and silver dollars at least should be primary herbivores.
Food might have been a problem--could have had a bacterial growth, or started to decay, and the smaller fish didn't eat enough? That's a very protein heavy diet--I'd add some veg. I know the fish will eat it, but barbs and silver dollars at least should be primary herbivores.
