A good rule to remember is NOT to prune things......plants USE all the stored nutes, minerals etc in those ugly leaves so if you yank them you do two things.....

1. You set the plant back by forcing it to now concentrate on healing from all those leaves you just yanked instead of growing so it's wastes both time and the plant's energy in an unnecessary way....not to mention stressing it's immune system as well.

2. The moment you yank them the plant will immediately start pulling nutes from the next set of nice green leaves since whatever problem it has is still there and you'll be in exactly the same boat......with less plant as well.

Have you checked the ph of your water and your soil runoff?