tank overhaul cleaning issue

[beginner reefer1]

so i put this tank out of commission a month or two ago after transferring everything living in it into a bigger tank and i wanted to do a full redo of the tank, considering it was my first tank i didn’t do a very good job at keeping the acrylic clean and there is coraline algae all over the tank as seen in this photo i want to fully clean the acrylic so its clear once again so i can start the tank back up but it just wont come off no matter what i scrape it with, i also dont want to damage /scratch the acrylic and would like to know if anybody has any strategy to get it off. other then 2 inch’s of water at the bottom the tank does not have any water in it.

trust me i’m aware it looks absolutely awful

 

[Aaron Stone]

Get the rest of the sand out, fill er up with tap, throw in some citric acid, and let it run for a day or two with the pumps. Coraline and other calcium carbonates should come off like butter.

 

[beginner reefer1]

Get the rest of the sand out, fill er up with tap, throw in some citric acid, and let it run for a day or two with the pumps. Coraline and other calcium carbonates should come off like butter.

how much citric acid are we talking, or does it not matter

 

[Aaron Stone]

1/2 to 1 cup per gallon.