Broad Leaf Swords

[Caro]

My broad leaf swords have big yellow spots (with brown spots in the middle) on them, and I mean the largest leaves have a lot of these spots.

Should I take all of those leaves out or let them be?

I've just added them to my new 20 gallon tank 2 1/2 weeks or so ago and some already had these spots but it seems to be getting worst everyday.

My tank came with a daylight fluorescent lamp of 15 watts - if that is any help - and is left on during the evening for 6-8 hrs. There is no direct sunlight to my tank; actually, the tank is set up in a corner of a room which is pretty shaded. I also give my plants the required Aqua Gro plant food which was recommended by the LFS.

Thanks for any help.