Well, while all of you are off on this tangent I tried your suggestion of adding root tabs.... and had an ammonia spike that killed my poor bamboo shrimp!! I had PERFECT water quality prior to adding the damn root tabs!
If I were you, I would take a deep breath, slow down, and regroup.
You've got a very newly cycled tank that does not have a mature biofield yet.
Some root tabs contain Urea, so you may have created an ammonia spike. What type did you use? And how many?
But really you need to be looking at the big picture. Just saying based on your comments about fertilizers and other things it seems you don't have a lot of experience, and your time would be well spent studying up on what makes planted tanks successful.
This site does a great job of explaining everything from the basics to advanced knowledge.
Like others have said, DIY CO2 on a tank that size is not a good idea. And when adding CO2 and medium light, you are driving the demands for ferts. I would read up on and learn to understand macro and micro ferts. IMO, right now your biggest problem is that your plants are starving.
Have you seen or followed any tanks that have similar goals and tank size to yours? If not, you should. Their success can be a blueprint for the types of things you should be focusing on.
Good luck and I hope things begin to turn around for you.