Algae explosion from filter

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Jun 17, 2019
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Hi all,

I'm a first-time poster here. I had a small 20 gallon tank with a handful of fish several years ago, but am just now getting into the hobby with both feet.

This weekend, I purchased a used 75 gallon system locally. Everything is in excellent condition, except the previous owner had some pretty good algae growth going on when I inspected it at his house. "No problem," I thought. I was going to give it a thorough cleaning anyway, which I did.

After a couple hours of elbow grease, I filled the tank to begin the cycling process. (I think) I knew it was important to establish the tank bacteria using his old filter media, so I left everything as-is and got 'er going. IT WAS LIKE AN ALGAE BOMB. As soon as that filter started pumping, my clean and clear new tank turned into a green cloud with about 6 inches of visibility.

Here's my question: What, if anything, do I need to do about the algae? I will be doing frequent water changes, but now that so much algae has been introduced into the tank, do I need to drain it and start over? I will eventually put in new/cleaned filter media, but what at this point? Thank you so much for sharing your knowledge and experience!

TL;DR: I installed a used canister filter and it pumped more algae into my new tank than I thought was possible. What do I do, if anything?
First thing, never use filter media from someone else's tank, only your own (some aquarists will not even do this, as each tank is biologically unique). Aside from the "algae" you have no idea what pathogens may be in your tank now. I would drain the tank completely, and toss out the filter media and purchase new media. If you have substrate and it is new, clean it well under the tap. If it was his, discard it.

Give the canister housing a very good clean (a bleach dilution followed by several good rinsings under the tap and then allow air dry completely before putting any media in it).

Cycling is the least of your worries, and there are safe methods to do this (the bacterial supplements like Tetra's SafeStart or Dr Tim's One and Only to name two very good products).

The green cloud is likely green water, the sign of high organics and thus very bad aquarium maintenance by the previous owner or else he just didn't bother knowing he was getting rid of the system.
Hi and welcome to the forum :)

Just drain it and wash everything out and start again.

Any beneficial filter bacteria would have died off while the filter was sitting dormant doing nothing so there's no real point keeping the dirty filter materials.

Wash everything in tap water or bleach it, including the filter materials. If you use bleach, rinse it well afterwards.

If you have any carbon (black granules) in the filter, then throw the carbon away and don't bother replacing it.

If you want to keep the filter media, bleach it or fill the tank with water and add a heap of rock salt or swimming pool salt. You want so much salt that it no longer dissolves and leaves a 1 inch layer of salt on the bottom. Turn the filter on and let it run for 24 hours, then drain and refill the tank. Let it run for a couple of hours before draining and refilling it again. Then set it up.
Thank you all for taking the time to share your experience and expertise. I posted a similar thread on another forum (not expecting such active communities!) and was given some excellent advice: "Whichever path you choose, it will be a bit of a PITA, so while doing the clean-up keep repeating to yourself 'I won't do THAT again!'"

Thanks again and I am excited to be a part of your community!

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