To add personal experience instead of the light rule I mentioned above... I have the same light and tank height as you (almost) and I had the same issue you did until my tank filled out with about 50% of it being plant mass.
I was just telling people how I went four weeks without a water change in another thread because I know my tank well enough at this point. I didn't fertilize in the last two. By the end of the fourth week, I JUST started getting algae and performed a very large 70% water change. Due to the type of algae that popped up (a couple black beard) my best guess was a dirty tank (very high TDS, other measurements OK), not unhealthy plants (per past experience). Made sense.
At that same moment I also cut off about 50% of my fast growing plants out. Guess what? A week later I had green spot algae for the first time in months (black beard dissappearEd so I knew the tank water was clean enough). I attribute that to the loss of plant mass and the reduced allelopathy to keep the algae away. Nothing else changed.
High, healthy plant mass = no algae. You don't have this yet.
Last edited by Ddrizzle; 07-21-2020 at 06:49 PM.