Is it new growth turning yellow or is it only on the old leaves?
How many hours of light are the plants receiving each day?

The last time I reveged a plant I had it under 24/7 light and gave it a good dose of high nitrogen fertilizer and it grew well, really bushy. The plant will definately need fertilizing as nutrients will be extremely depleted after flowering. Repotting into a bigger pot will help a lot too.

Hope this helped

GC