How many almond leaves should I add to my tank?

[Nicki Gaga]

I've got a few almond leaves that are around 20cm (I think they're medium size). I've got a 24 gallon tank and the filter contains a nitrate, fine and polywool sponge and I would like to breed my tetras. How many would you suggest to put in until the water turns brown? I've added 4 already and I don't want to waste them by putting in too much

So how many would you recommend? The leaves have been in there for 2 weeks now and the water is still really clear.