It's BBA, and you are likely low on CO2. Your PO4 is fine but you are low on NO3 too. What amount of K and Fe are you dosing?
You are also growing slow growth plants that don't need the amount of light you are giving them.
GH boosters contain extra K, and should not be used. I would just use magnesium sulfate and calcium sulfate to set GH. If your livestock allows, drop GH to 5dGH at 2:1 Ca:Mg.
I would thoroughly read through all of this to better understand what's going on.
https://www.2hraquarist.com/blogs/choosing-co2-why
Here is how I'm currently dosing my tank. Notice the PO4 dose.