You can put as many in as you like as long as they don't cause a sudden drop in pH, and as long as they don't turn black. If the leaves start turning black, they are anaerobic (lacking oxygen) and the fish will probably suffocate.
Two leaves in a 45 gallon tank won't do anything.
If you want the leaves to add tannins to the water, put a bunch of leaves in a container with some dechlorinated water and add an airstone. Leave the leaves in the water until the water starts to turn brown, then remove the leaves. You should check the pH and ammonia of this water before using it in an aquarium.
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If you have room on your property for some deciduous trees like European Oak, you can collect their leaves in autumn and use them instead of Indian Almond leaves.