Join Date: Apr 2012
Location: Vancouver, Canada
Don't get frustrated, it is just that this could be so many things. I will just shot gun it for you as it comes to mind. Low GH could come in the form of low calcium, which produces small shriveled leaves, or low magnesium, which produces very white and easily infected growth. What I mean by easily infected is it is taken over quickly by algae like GSA, BBA etc.
If your plant leaves are falling off at the root, i'm assuming it's not a stem plant first of all. Maybe a Val or crypt? Again, you would have to be more specific in your question.
Having something melt at the root could be because you berried the rhizome into the soil or substrate. It could be because you moved the plant, and now the roots cannot support all of the leaves it could previously.
Ruling out all of the above, if it is a root feeding plant, pick up some root tabs from your LFS and try them out. I have had jungle Val show a similar problem as what you're describing. I tried moving the plant to different parts of the tank to give it different light. My other plants were doing just fine, but this one wasn't really growing and would lose leaves at the base. Then I put down a root tab directly under it and it started giving me rapid new growth.
Remember that certain plants, like jungle val, grows from base up. If a leaf is melting at the stem, it can mean a lack of nutrition for the new growth. This would produce a weak spot as you describe. If the rest of the leaf is green, then all that means is while that portion was growing, the plant had sufficient nutrition.