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Brown Stains in Tank

Subject: Brown Stains in Tank
by Busgrw on 3/2/2021 20:06:59

Hi all,

First time posting here and looking for help.

I recently (2 weeks ago) bought 3 goldfish for my kids and there seems to be some form of brown discolouration or staining on the stones and the filter of the tank. Please see attached picture of stones.

Any thoughts on what this might be and how to resolve?

Thanks in advance.