Algae Growth

[Jaws]

Scenario:

Over the last two months I've had some hair algae starting to grow all over the display tank. I've got a pretty huge bioload but I also have a lot of equipment running to control it like 2 large skimmers, 1000 ml of all in one biopellets, and a refugium running lots of live rock and macro algae. The display tank is 400G with 600G total water volume.

Almost a month ago I added another 1000ml of biopellets. The chaeto in the refugium has died off completely but the caulerpa has stayed alive although it isn't growing. The hair algae still hasn't shown any sign of diminishing but instead I started seeing some of my LPS start to die off slowly and some of the SPS start to really lighten, kind of resembling lack of nutrients.

Then I realized a couple weeks ago that half of my T5 lights are almost a year old. So I swapped them out this weekend as well as replaced my DIY LED lighting with Ecotech Radions.

I should also mention that the frag tanks and the refugium don't have any hair algae growth in them and they have much slower flow. So do you think this is just a case of old/bad lighting or does there have to be a heavy presence of nutrients for the hair algae to grow in the first place? If you think it could be lighting, how long does it usually take for algae to start dying off once lighting has changed?

Thanks for your help