I've got a whole packet of JBL root tabs scattered around the substrate of my tank, i couldnt tell you if they are helping or not though.
Cabomba is a horrible plant for a tropical tank in my opinion, i did try it, but for me it rotted at the base something crazy and when i pulled it out, hundreds of bits broke off and i spent ages netting it all out. Not something i will use again. Vallis grows well for me, but thats because i'm in a hard water area (so im told), however, it used to melt before i started using CO2....
How much light do you have over the tank and for how long?