Green hair alge in and of itself is not bad. The reason most people don't want it is it is ugly and, if fed enough, grows worse than morning glory. As far as affecting parameters, it will not cause your parameters to be off, it will indicate if they are off. If you have a sudden explosion of green hair alge, or any micro alge for that matter, it means there is somthing wrong. Whether it is from over feeding, water too hot (this is also usually indicated by your fish floating upside down at the top of the tank as well,) or somthing in you tank died, it is just an indicator. If you figure out the cause you can get rid of the alge, but as far as it being on your return, don't worry about it. Just trim it back when it gets too bad
