I just bought this product online meaning to get the regular flourish and I am a little bit scared to try it. I think it can be harmful to fish, especially if i add to much. My twenty gallon has had some algae growing on the Java ferns that looks like fine black strands and I was hoping this would clear it up though. I am already using flourish tabs and API leaf zone (the bottles almost empty and I wanted to replace it). I am not sure If i should use it or try to return it... Mostly because I worry compulsively about my fish. But I also want my plants to be really beautiful.