Green water algae is usually caused by ammonia, probably from the relatively fresh soil. So it might be just because you tank isn't really "mature" yet. Diatoms is also regularly seen in new setups, and go away by them selves after a couple of months in most cases.
If there is actually growing algae on the substrate, which seem like green dust/powder is, well, green dust algae
Often brought on by too much lights for the tank.
If its was me, I'd be doing 2-3 50% or more water changes pr week for 2-3 weeks and just wait to see if it improves after some more maturing. WC will help diluted organics in the water, remove algae spores and dilute ammonia if it is present. You might not even be able the measure the ammonia, but the algae doesn't need much to grow. All these things will help restrict algae growth, but not stop it completely. Only a big healthy plants mass with a tank in balance can do that. Which is what we all strive for.
The planted tank "god", Tom Barr, has only been able to produce green water bloom with ammonia, so thats where my reasoning is coming from. Green dust I had quite a lot of my self. PS BN pleco's and Oto's will demolish Green dust and diatoms.
As long as your plants are growing and not having algae grow on them, I'd say your on the right path. Just give it time.
If there is algae on plants, that's a sign that they are not super happy. Then it's a matter of balance between lights, ferts and Co2. 99% of the time a Co2 issue, but it might be something else.
Edit: Regarding the other persons tank, doing the walstad method too with a much "cleaner" tank than yours. Without co2 and ferts, might be just down to lower lights. You have pretty high light, and doing more or less a high tech Walstad. Light drives co2 uptake, which again drives ferts uptake. Low lights = low demand for co2. Low co2 uptake = not a lot of ferts needed.
2 T5's with ok reflectors would be about 40-50 par at substrate, so about medium lighting. And this would definitively require some Co2 and ferts for no algae and happy plants. If the soil is enough on it's own, I'm not sure. Never done walstad. But the walstad's I've seen is usually pretty low tech, and have even less lights. 1x t8/t5. Somewhere between 15-30 par would be my guess.