Hair algae does not need to "migrate". Algae will grow where the conditions are right regardless of any exposure to other algae. IE you can grow excessive amounts of hair algae in a brand new system (and often do).
So if you have nutrients (which you must have), and enough light (which you must have) ,it will grow
. So the goal is to have enough nutrients to grow some (too little and corals will suffer), but have things that will keep it in check like snails/crabs etc to the point where it wont take over.
I agree with the person above...use your algae as a measuring technique...NOT test kits. Test kits are a waste of time/money IMO when it comes to this. You know you are not 0/0 when algae is growing. The best method I have for relative nutrient levels is your glass. If you need to clean your glass more than every 2-3 days, you probably need to reduce the nutrient export of your system. Bottom line, algae cannot/will not grow if you dont have No3, Po4 AND light. Its like the fire pyramid
. Remove any of those, and it wont grow. You have all three my friend....
As do I
For reference, I used to use Zeo too, with much success (and much $$ spent). This go around I am going more natural, and added an Algae Turf Scrubber, and hoping that will turn my tank around (Currently my display is riddled with HA). If I cant do it naturally, I will defer to what I know and that is Po4 Remover and Aggressive Carbon Dosing. Both worked for me in the past