Firstly,as everyone else has stated, you need to be more specific with the typre of plants.
where did you purchase plants from??
My first thought is the plants have been grown emersed(out of water) and need to be acclimatised to being submersed.
Secondly, you say you are giving them heaps of light. Well how much? what type of lights are they, what watt, what is the depth of the tank.
Artificial light is nowhere near as bright as the sun and most plants require a fair amount to grow healthily.
Feeding plants ferts is no good until plants have established and roots system has developed. But again its had to say as you have not ID'd the plants in question.
Answer some of these questions and we will be able to help a bit more.