Holes in lily pads

[WBAC88]

I have both dwarf lilies and banana plants in my planted 65g tank and I've recently been having the trouble of their lily pads developing holes, eventually to the point where they've almost rotted away. I dose Excel daily and Comprehensive weekly after PWCs and it seems like all of the other plants below the surface of the water don't exhibit the same problems. They have some algae, but that's about it. I've read here that low nitrogen can cause holes to develop in leaves and testing today, 1 day after a 50% PWC, there were no nitrAtes to speak of in the water. Any body have any suggestions for this? I love having the lily pads on the surface, but it's unsightly and obviously unhealthy to have them rotting away like that. Thanks!

 

[aqua_chem]

You can easily bottom out on nitrates if you have decent light and fast growing stem plants.

 

[WBAC88]

You can easily bottom out on nitrates if you have decent light and fast growing stem plants.

Are there any nitrogen supplements that I can use to help stop this from happening? Or what would be the best way to prevent this?