blank wandered in from the void and babbled something like:

Having managed to finally eliminate the hair algae in my 75 gal tank (no
CO2, low lighting), I added just 2mm of Seachem Flourish Iron to the tank
and within two days the damn algae is coming back. Is the fertilizer
encouraging this? Or am I barking up the wrong tree?

It has been suspected that algae outbreaks may be caused by high iron
levels. That would be levels so high in relation to other nutrients
that the plants cannot use it before the algae takes hold. Algae
tends to be very opportunistic...