I can tell you I tried it a few years back. Everyone I had seen posting was getting great results within 2 weeks. I didn't have such good luck with it. I went 2 weeks no change in hair algae, 4 weeks no change, then 8 weeks no change and then I started getting rtn. I lost 6 coral frags all of a sudden in a two day period. I stopped dosing the Algaefix Marine immediately and did not lose another coral. That was the only thing I could contribute it to. Not one other person had those issues but like I said, everyone else that got good results saw them within 2 weeks. I would say just be careful if you don't start seeing results in two weeks if you use it. The other thing is that it's a band-aid and if you don't correct your excessive nutrient problem, the hair algae will just come back.