Questions about Indian Almond Leaves

[Auratus]

Ok, so I'm looking at some on ebay but I don't know how many to buy. Are these leaves a one use thing? And do you use a whole leaf per certain amount of water?

I can get:
100 for $20
15 for $5
25 for $7
50 for $13

How long do they last? Do I have to put a new leaf in everyday? hehe... I dunno these things. Should I just go ahead and buy 100 leaves?

 

[BettasRFriends]

IMO I believe it's better to buy the 100 leaves. I've been using IAL for a while now and I think it's a one time use. 1 square inch of leaf = 1 gallon. Anyone wanna pipe in a give me a hand here?