BBA is an indication of insufficient CO2, 5bbp is not too much for a 100g, especially for 4wpg of light, assuming you have T5. that's too much light. i have 5+ for my 72g, which only has 64w of T8 of it. it also depends on how efficient CO2 is diffused into water, and how well CO2 is distributed (water flow) in the tank.
here is my tank with less than 1wpg of T8.