What brand of root tabs do you have, some root tabs, the cheaper ones only last a few weeks and can release their content into the water column which can affect livestock, the better quality ones normally cost a little more but worth it as they last at least 1 month to 6 months, dependant on what plants you have.
I personally use Seachem Flourish Root Tabs and these generally last about 2 - 3 months before replacements are required in the substrate.
Other decent brands like TNC mentioned earlier varies but can last anything from 3 - 6 months is the idea.
Swords are nice but remember they do grow pretty big and they can last for years under optimum conditions. Not suited for the smaller tanks imho.