for the lighting gurus on pt, would 247 watts or 3.29333 wpg be enough light to grow say... blyxa japonica and hc with everything else such as co2 and fertilizing being in order, over a 75 gallon that is 18in tall?
More than enough. The larger the tank, the less overall light it needs. The factors that play the most significant role are intensity (light type itself & proper reflectors) and coverage. Your goal is to use light efficiently, not bombard the tank with sheer wattage.
I'm growing blyxa and HC in my 90g that's running 216w (2.4wpg). Don't worry about the wpg rule for larger tanks. It really doesn't measure up.
ah supply kits are pretty good and the reflectors are about the best there is. I'd say you could get away with even less.