Java fern problem

I have java ferns that used to grow and propagate rapidly to the point where I started throwing them away, but for the past few months they are gradually turning brown on some leaves and dying. Also, my sword which has flowered is growing new plants, but they look weird like pieces of the leaves are missing. I use Excel and have been dosing Plantex and potassium at water changes. Any idea what deficiency this may be indicating? My anubias and crypts are doing well.

 

Yes, sorry, it's CSM+B. Nitrate and phosphate are both somewhat high anyway now so I haven't been adding any (high fish load, heavy feedings) This problem has actually seemed to have gotten worse since I started using Excel (from non-co2). That's why I was thinking it may be nutrient related. I had co2 in the past on and off and my java ferns were the only plants that seemed totally unaffected by the fluctuating levels of co2. I stopped because I was sick of diy and didn't want to invest in a system. It's about 25 gallons of water and I'm adding close to a capful a day of Excel (a capful being the standard dose for 50 gallons). I'm afraid to increase it any more than that.