It's true there is a very, very small risk of introducing diseae with media from another tank, but poor water quality kills more fish than anything else, so it's worth the risk. tropical media will work just as well in a coldwater tank.
I should point out that fish don't need to be in glass boxes; that's just for our convenience of looking at them; your fish need a larger amount of water; you could buy yourself a cheap plastic storage box from a DIY or supermarket that would be better for your fish while you look for an upgrade.
I should point out that fish don't need to be in glass boxes; that's just for our convenience of looking at them; your fish need a larger amount of water; you could buy yourself a cheap plastic storage box from a DIY or supermarket that would be better for your fish while you look for an upgrade.

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