Hi there
Nitrate of 8 is ok as for your hair algae there could be a number of reasons usually to do with higher phos readings along with nutrients building up,
also lighting contribute towards it too i.e. The wrong spectrum or too long a period.
So do you test for phos do you do water changes how big is your tank what type of lighting do you use a protein skimmer what do you use for circulation how many fish do you have I could go on and on really you need to give us a more in-depth on how are your system runs and how big it is you get more of an idea,
In the meantime IMO The simplest route to reducing hair algae without chemicals is to start stripping it out by hand and increase water charges making sure your fresh water is three of No3 and Phos before adding to your system.
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