Good thing it is still just a minor hair algae problem but they can grow quickly if you leave them unchecked. Hair algae consume the nutrients efficiently that nothing is left for your test kit to read. The cause is over feeding and lighting. First thing you should do is physically remove them and get some cucs like turbo snails and hermit crabs. If your tank size would allow, get a yellow tang. They love to nip on hair alage. Lastly, cut down the length of time for your lights.