After going through a period of frogbit overtaking the tank it seems to have started dying off. This started several weeks ago and is a mixture of leaves melting, getting holes and generally dying off. I don't think anything has changed in the tank and I have doubled ferts over this period without much impact. The only thing I have noticed is the amanos spending more time in the frogbit than before (but not sure if this is because it is in poor condition or whether they are submerging it and causing the poor condition). I did also add some Ramshorn snails a while ago but I don't really see them on the frogbit. Other than upping ferts even further could there be some little detail I have knocked out of kilter or perhaps could it be seasonal with there being more condensation under the hood as it is colder outside the tank?