Yeah, it'll be a struggle to keep BBA off the HM without co2 IME. Been there, done that. HM grows like crazy once it gets settled in. I was growing some in low/medium light and it took over the tank... got about 4" thick across the whole tank bottom. I had some in my 40b with 2x39w T5HO and had to spot treat BBA with H2O2 almost daily.
Root tabs aren't going to do much, if anything, for HM. You would be best off purchasing some dry ferts, or even paying for water and buying a pre-mix like Flourish Comp.