How long?

How long is it gonna take them to turn brown?:

It may not turn brown. I think they need to be brown before you pick them? But I'm not sure

JuiceBox52 said:

It may not turn brown. I think they need to be brown before you pick them? But I'm not sure

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They should turn brown
I'll wait for @Byron and see what he says.

There is a difference between leaves that come off the tree when green, and leaves that actually die while still on the tree, then fall off. The latter are void of any tree sap, at least that is my understanding. I'm trying to think back, but I don't believe I have ever seen leaves that come off the tree when still green and turn brown, they just sort of wrinkle up a dark green, as in the photo above..

Byron said:

There is a difference between leaves that come off the tree when green, and leaves that actually die while still on the tree, then fall off. The latter are void of any tree sap, at least that is my understanding. I'm trying to think back, but I don't believe I have ever seen leaves that come off the tree when still green and turn brown, they just sort of wrinkle up a dark green, as in the photo above..

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So they won't got brown and be safe for my tank?

Salty&Onion said:

So they won't got brown and be safe for my tank?

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I don't think they will turn brown, but they might. As they did not die on the tree and then fall, I would not put them in a tank with fish or invertebrates. But that is just my caution when it comes to things going in a fish tank, and of course the tree species is a factor if it is toxic or not.

It is always better to use caution when adding natural materials to an aquarium. In nature, something toxic (thinking natural objects like leaves and wood) getting in the water is not likely to kill the fish because the toxin that leeches out will be carried away by the water current or dissipate in the expanse of a lake, etc. In an aquarium, there is no where for such toxins to go but in the fish and invertebrates.

I am reminded of an issue told to me several years ago by a professional biologist. He collected some dwarf cichlids in a stream in South America, and because this particular species needed leaves as spawning sites, he collected some of the dead leaves that were on the substrate in the same creek where he caught the group of cichlids. Brought them back to Vancouver and set up the tank, put the leaves in to litter the substrate, and added the fish. All seemed fine for several weeks, until suddenly the fish all began to die, within a very few days. Test after test revealed nothing, until it turned out the leaves were naturally toxic and this substance had leeched out from the dead leaves. In the wild, not a problem because of the expanse of water and the toxin being carried downstream, but in the confines of the aquarium it was deadly.

There is such a thing next to my house as a "community garden" (but people treat it as their own ) and there is a hole between the wall of the building where the leaves are, there is also a wooden fence. Behind the fence is a factory with a car park where lots of cars and motorbikes drive by and stop by. On the left, is a car park for the building. The "community garden" is about 40 ft long and the leaves are placed in the middle of it.
The leaves have fallen from the maple tree (they are brown 100%, and they are also behind from months ago) that is behind the wooden fence and its other half pointed on the garden where the leaves have fallen.
Do you think they will be safe?

Salty&Onion said:

There is such a thing next to my house as a "community garden" (but people treat it as their own ) and there is a hole between the wall of the building where the leaves are, there is also a wooden fence. Behind the fence is a factory with a car park where lots of cars and motorbikes drive by and stop by. On the left, is a car park for the building. The "community garden" is about 40 ft long and the leaves are placed in the middle of it.
The leaves have fallen from the maple tree (they are brown 100%, and they are also behind from months ago) that is behind the wooden fence and its other half pointed on the garden where the leaves have fallen.
Do you think they will be safe?

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If it were me, I would head out to a forest and pick up dead leaves in the autumn. Or maybe now...I came across something a while back about not using dead leaves that had over-wintered, but I don't remember why or where it was. My back yard was safe as there was no industry within miles, it was secluded, and I used no fertilizers, pesticides, etc.

Byron said:

If it were me, I would head out to a forest and pick up dead leaves in the autumn. Or maybe now...I came across something a while back about not using dead leaves that had over-wintered, but I don't remember why or where it was. My back yard was safe as there was no industry within miles, it was secluded, and I used no fertilizers, pesticides, etc.

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Yeah, forest maybe a park would be much better. Thank you for all your time