As you know, we're about the biggest fans of using leaves in aquariums as anyone out there. We've utilize large quantities of a significant variety of dried leaves in a lot of different aquarium situations, and we've developed quite a "feel" for the characteristics and applications of them.
We've gotten to the point where we are fairly comfortable recommending approximate "numbers per gallon", types you should use, and the most controversial topic related to leaf use in the aquarium, how to prepare them for use in the aquarium.
I'll be the first to admit that we're pretty conservative when it comes to the preparation of leaves for use in aquariums. As a matter of practice, I recommend rinsing them, steeping them in boiling water for at least 10 minutes, and then an overnight soak in freshwater before tossing them in your tank.
I have actually received some criticism in some circles for recommending this practice, having been told by a number of hobbyist that steeping leaves in boiling water before use is unnecessary, that it is being "overly cautious", and actually and will "deplete a lot of the tannins" bound up within the leaves. This is the "rinse and toss" crowd, and they report equally successful results by applying this technique.
I freely admit that I have employed the "rinse and toss" technique with a number of different leaves, and have never experienced any difficulties, in terms of disease, obvious pollution episodes that could be attributed to the non-steeped" leaves, or other obvious phenomenon, like cloudy water, etc. However, I also can tell you that I've seen no real difference, from a visual standpoint, at least- in terms of the tannins released from fresh leaves as opposed to steeped leaves. Besides, who has the test equipment to measure this, outside of the lab? We're really relying on visual observation and even "feel" as hobbyists, right?
Oh, sure, I agree there is probably a loss of some of the "initial tannins" bound up in the outermost layers of the leaf tissue ( the cuticle or maybe the upper epidermal layer), but I doubt that the steeping/soaking period that we recommend can thoroughly break down most leaves to the point where they lose significant tissue, and therefore, the tannins bound up within.
In fact, I wonder, how much tannins are really bound up in, say, the cuticle, the leaf structure most likely affected by steeping and soaking. The cuticle is the waxy outer layer of the leaf, responsible for preventing water loss and keeping out pollutants. It's thickness increases depending upon how much light exposure the leaf is exposed to. I think it's more of a "sunscreen" than anything else, and really doesn't contain much in the way of tannins. The epidermis, on the other hand, is where a lot of the tannins are most commonly found. Typically they are located in the upper epidermis and mesophyll layer in most leaves ( However, in evergreen plants, tannins are evenly distributed in all tissues).
Does a 10 minute steep in boiling water break down the epidermal layer of the leaf to the point where all of the tannins "leach out?" I don't think so. In fact, in my discussion with a few botanists, they felt that a steep in boiling water would soften and dissolve parts of the cuticle of the leaves, enough for some of the epidermal tissue to be more exposed, but that's about it. As one put it, "There will still be plenty of tannins left to go around!"
In fact, water is a good "solvent" for getting tannin out of the leaves over the long term , but not as quick or efficient as chemical solvents like a 30% solution of ethanol, or even acetone, which I read about in one study as being the most efficient means to extract tannins from Guava leaves (Yeah, you're NOT going to use ethanol or acetone...). So the reality is, you will lose some tannins by steeping in boiling water for a few minutes and soaking for a day or so, but consensus of the botanists that I talked to is that the amount is relatively trivial compared to how much of this material is typically bound up in a given leaf.
In addition to creating a little piece of mind for you, steeping and soaking the leaves before use will at least release some of the pollutants (i.e.; dust, dirt, etc.) repelled from the internal leaf structures by the cuticle, giving you at least a slightly more "hygienic" leaf to add to your aquarium. And, being a bit more saturated with water, it's likely that the leaf will sink immediately in the aquarium, and possibly begin breaking down that much more quickly.
So, yes, I confess- I have simply rinsed and dumped my leaves before without incident. In fact, I've done all sorts of crazy experiments with botanicals that I'd never recommend anyone try- in the interest of developing "best practices", and ascertaining which botanicals are safe to use in our tanks. However, as a responsible aquarist and a vendor who earns his living from selling these products, I owe it to everyone to relay information which I feel is the best practice for the widest variety of aquarists. Being honest and responsible is not just about "good service", it's about relaying advice based upon what I have practiced.
At the end of the day, as they say- the choice is yours on how to best prepare your leaves for aquarium use. It's definitely more of an art than a science, and that's the fun part. However, as a matter of "best practices", we're gonna stick to recommending the "steep and soak" process for now. On the other hand, if you're a "rinse and toss" kind of aquarist, we're certainly not gonna hold it against you!
Regardless of what preparation method you employ for your leaves- be consistent. Stay alert to what's happening in your tank...Share your observations. Refine your techniques.
Stay focused on the fun. Stay enthusiastic.
And Stay Wet.