When you say that you've had these plants for about 2 months, is that the time when the whole tank became planted? Or did you have other types of plants before? The reason I ask is because of my own experience. My tank first started with only plastic plants. As time progressed and the tank became more established I began add plants and they thrived. They held their own for a good number of months before they began to show signs of deficiencies. What I figured is in the time frame they were using the nutrients available in the tank and when they started melting the nutrients were gone. I can say if the is an amazon sword I gave my root tabs and it grew taller than my 18" tall tank.