Another what is this algae?

[jimbo_natale4]

Low/mid light, goldfish tank, good filter, gravel substrate... the algae is green and hard to get off... what is this algae? Also side note::: do tanks under go seasons? Because during the cooler months of the year I get a lot of algae that shows up as well as in the spring. But over the summer I am mostly clear of algae.

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