I seem to be having the same thing and within the last week or so its been unstoppable. (see pic)
I spent 3 hours this morning cleaning it out and did about a 60% WC. Dosed excel with initial dose according to bottle afterwards, woops?
Tank is new as well, about 30 days.
Should one avoid ferts while this is occurring? I stooped dosing for about 3 days last week, but the plants really started looking bad, and I thought, well its better to have healthy plants and algae instead of dead plants and algae.