I used to think that it was luck too. I could have sworn that the Iron dosing was causing the hair algae problems I was seeing. It kind of was, but like Tom said because of low nitrate levels. At the time I thought that Nitrate and Phosphate caused algae so I was keeping these at 0 ppm, but was dosing around 10-15ml of Flourish Iron in my 55 gallon. Fast forward now: I'm dosing 25ml of Flourish Iron a week for the last 3 months now with weekly 50% water changes and have absolutely no hair algae problems. The difference now? 10ppm Nitrate and 1- 1.5ppm phosphate.