i would personally never add any chemicals.The reason you have algae is either you have phosphates from not using research grade carbon,you arent doing a 20% water change every week,overfeeding,if you use frozen foods you must strain the food out after you thaw it and get rid of the juice,the juice is like fertalizer to algae,or your levels are off.I would never add any type of chemical to a tank unless it is a quarantine tank and even then im skeptical.a smart caveman once said water changes good chemicals bad.Take anthony calfos adivce and dont use chemicals!!!!