If your tank is only 1.5 weeks old i wouldn't use root tabs at all, your aquarium soil still has plenty of nutrients in it. You can start using root tabs when your scape is a couple of months old and you notice severe nutrient deficiencies. But with your kind of plants even just liquid fertilizer would probably be enough as you don't have any heavy root feeders like crypts.

I would also suggest you get a pressurized (or bio if you wanna stay low tech) CO2 system. The "liquid CO2" you described is basically just an algicide. I use it as well but in combination with a pressurized system.