I get some in mine too, the Shelly tank, in my case, is the only nutrient/mineral rich tank on the wall. All the other tanks, left soft, have enough plant competition to choke out any filamentous algae and the lack of calcium prevents the spot algae that occasionally occurs from getting hard so it's eaten. The Shelly tank is the only one that makes crunchy noise if I use the algae scraper, and it seems to harbor a decent amount of hair algae if I allow it. Even with my Shelly tank being moderately planted (75%+plant cover) with moderately high lighting and enough (over)stocking to provide adequate CO2 naturally my plants cannot out perform the pesky green stuff. I don't recall, do you also have soft tap water (in your other tanks)? That really does help keep the algae down, I've come to realize I have been spoiled in that regard.
Updated: Today I cleaned the glass my Shelly tank and cut a leaf from the anubias to analyze. The lower leaves black spotting is under the skin of the leaf, they still feel waxy and full. I do believe it's burning from when I switched to hard water, and increased the brightness in the tank close to simultaneously. All the upper clean growth is new since the changes and it's pretty healthy. The growth rate of this anubias (3 years old in soft water) increased by several hundred percent upon hardening the water and increasing lighting, the rhizomes doubled in length in 6 months.
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The only ones looking forward to me finishing the 55s more than me are these little guys lol.
