Did my tank crash! Help!

[Sasq40]

I got the tank used a a few weeks ago and was looking a little rough when I picked it up, had lots of hair and cyano. So I've been doing water changes to bring and down and it's been working.
And yeah I should have done a lot more but I trusted he knew what he was telling me cuz his tanks are beautiful. I could have misunderstand what he said to so I'm not going to just through him under the bus. I got the kalkwasser from jl it's the bigger container they sell. I had around 12 tbsp in 13 gallons of ro/di and was thrown in over night with my ato

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