I have been trying, off and on, to grow this accursed plant species for the better part of 40 years. It
always does that! I have never been able to produce the sort of beautiful specimen that you see in the pics; mine always start out great, because I select carefully, and then they slowly, gradually decline into the sad disgusting mess in your pic. They will produce new leaves, and often the leaves will be crowded with baby plantlets...but those never grow.
tlindsey
has repeated one of the many suggested treatments and solutions I have heard over the years. None of them work for me.
I'm pretty certain that I warned you about this vile fern in another thread sometime back, when you mentioned you would try it. It's a guaranteed-to-die species; it just does it so slowly, so gradually, that it lulls you into a false sense of security. It's bound to get better, isn't it? No! It will just turn black and die so slowly...so gradually...no dramatic turning-to-mush, no painful-to-watch "melting"...until one day you look into your tank and there is nothing left of it. All the plantlets, all that hope for the future...poof! Gone!