new tank

I upgraded the old tank with new one about 4 months ago.
Old one: 45Gal, 2 40W GE plant lights.
New one: 100 Gal, 4 40W GE plant lights.
Basically, I have made no change except the tank, light and gravels. I 
just moved the plants from old tank to the new one. The plants were 
actually doing much better in the new tank for about 2 months. Since 
then, they started being bad ( growing slowly or not growing ). And I 
started having algae problems. I have been adding liquid Fe fertilizer 
regularly. The only reason that I can think about is that the new gravels 
had some important ingredients and they are now exhausted. Any comments 
or suggestion will be greatly appreciated.