Plants require fertilizer/nutrients (along with light and CO2) to grow. So yes, you need some way to get them those nutrients. You can dry dose (cheapest), use off the shelf liquids (you're paying for water), make your own, etc.
There are some stickies in the fertilizer and water parameter forums. You will need to make a post with your tank size, plants, lights, CO2 or excel, etc. for other people to help you out.
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