I have not used either product and would regard them with a degree of suspicion.
Brown "algae" is usually not algae in fact. Rather it is produced by diatoms, and is often a sign of low light. It is not unusual to get a diatom bloom in newly set up tanks if that is the case.
Adding CO2 will not have much affect if your light is very low. It tends to be the high metabolic rate, fast growing, high light regimes that benefit from CO2 addition.