Ok here is my newbie/rookie mistake.
Photo is of my first ever attempt at a saltwater tank back in like 2012. I practically screwed everything up on my first tank and I shut it down after like 5 months.
I did barely any research before jumping in and made a ton of rookie mistakes:
-bought a column tank with all four sides tempered glass.
-bought a used cannister filter and used that. It died like a month in.
-no protein skimmer
-bought used rock and didn't cure it.
-aquascape was firmly up against the glass on three sides
-lastly, the tank was placed in a spot where it got focused sunlight for most of the day.
In like a month the tank just exploded with green hair algae and I shut it down after a couple months.
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