Welcome to the Planted Tank!
A little planted tank can be very rewarding, but is also very challenging to achieve a balance, especially if you are planning for high light, CO2 and fertilizers.
What wattage is the current screw-in fluorescent bulb? Using a higher wattage bulb might be a cheap solution, but you should try to find one that has a "Daylight" color (~6500K) rather than the usual warm-whites (~3200K).
Is there some kind of filter on the tank? Some of the little HOB filters like AC Mini are actually pretty convenient reactors, you just bubble the CO2 into the inlet.
I suggest to not add any fish until you have reached stable pH levels.