minime, are you using tapwater, or distilled?
Some people use tap with no problems, I used it for years. It really depends on what's IN it, as I found out. I just about died when I tested phosphates off the charts last March. Nitrites, too! 8O in tapwater!
I switched to DI water, and haven't looked back. Hell, I'm afraid to switch back now. I don't even drink store bought springwater, I drink tap. But I will die and rot in hell before I go back to using tap on my reef tanks.
The algae aggravations were just not worth it. I'd rather lug water thru snowdrifts barefoot, uphill both ways! 8)
Just a thought.