When we add leaves and other botanicals to our aquariums, it's an absolute "given" and a known quantity among our community that these items begin to soften and break down, ultimately decomposing after prolonged submersion. This is part of the game; the "process" of keeping a botanical-style natural aquarium system.
Now, some of you really like the idea of the botanical materials looking pristine and fresh, and the idea of them or anything softening or breaking down in your tank is, well- not a happy thought! It's all about keeping a fresh-looking set of materials in your tank, with little decomposition or degradation of the botanicals....
What does that mean to you, the hobbyist, on a "practical" basis?
Well, it means that you're going to have to remove and replace your botanicals on a much more frequent basis than a hobbyist like me, who relishes the decomposition that occurs as a result of prolonged submersion in our tanks. What, exactly can you expect to see?
Leaves are among the most "ephemeral" of materials we use in botanical-influenced aquariums, and are the first materials to break down in our systems. Initially, you will typically see them "recruit" biofilms or fungal growths on their surface tissues. The extent of the blooms and the duration of time they are present will depend on a myriad of factors, ranging from water chemistry to leaf type to fish population.
As far as the physical "metamorphosis" which leaves go through when submerged is concerend- it's a fairly predictable process: Typically, leaves will start to darken, "curl up" around the edges, and ultimately, start breaking down, as bacteria and fungi act to consume them. Fishes picking though them don't exactly help the "preservation" process, either!
Some leaves, such as Catappa and Guava, will typically soften and break down after a month or less. Leaves such as Jackfruit, Artocarpus, and Magnolia will tend to hang on a bit longer, often recruiting significant quantities of the aforementioned biofilms and fungal growths on their surfaces along the way long before breaking down. The real "long-duration players" are Mangrove, Bamboo, and Live Oak, which tend to last a very long time submerged- often several months, in my experience...and typically not recruiting as much biofilm as say, Jackfruit or Magnolia.
Obviously, along the way, leaves will impart chemical compounds, including lignin, sugars, carbohydrates, cellulose, and of course, the coveted humid substances and "tint-producing" tannins, during their submerged existence. The important thing to ponder when using leaves is that you're likely to see an initial "burst" of the desired and less desired compounds shortly after they are submerged i the aquarium. The extent and degree to which these compounds are imparted to the aquarium depends on numerous factors (environmental conditions, the age and condition of the leaves, the presence of "shredders" snd "grazers" in your tank), and the extent of your preparation process.
As you know, we tend to recommend a more thorough preparation process, which involves steeping or even boiling your leaves before using them in your aquarium. This is an important part of the process of utilizing these materials in the aquarium, because it "sets the tone" for how your system will commence its "evolution" process. Steeping or boiling of leaves helps rid the leaves of dirt, dust, and other surface pollutants on the outer tissues of the leaves, and breaks down/soften them a bit to assure greater saturation and to facilitate easier "sinking" when immersed in your tank.
Now sure, you'll often hear hobbyists suggest that "you'll lose some tannins" when you steep or boil leaves before use, and that "Nature doesn't boil leaves before they fall into the water..." Although there is a grain of truth to these arguments, they're pretty weak, iMHO. Why? Because they overlook the fact that leaves (and all botanicals, for that matter...) are the "atmosphere-facing" part of the trees they come from, and as such, will accumulate the most significant quantities of pollutants- all of which end up directly in your tank if you just "toss them in."
And my experience over almost two decades of playing with botanicals in aquariums is that the amount of tannins (those which can be confirmed by their visual impact on the water color, anyways) "lost" as a result of preparation is minimal. Remember, the leaves will continue to release whatever compounds (including tannins, of course) which are bound up in their tissues for the entire duration of their presence in your tanks.
And of course, the closed-system aquarium is not like Nature, were there is a constant influx of rain, flood water, inflow from other aquatic systems, etc.- and thus, any pollutants and other compounds introduced into the aquatic environment via leaves or botanical materials are effectively "diluted" by the vast quantities of inflowing fresh water. And of course, Nature has "capacity" (the biological/chemical systems in place) to process the influx of these compounds, whereas a closed system aquarium might not...
So, yeah- THAT'S what we prepare our materials before introducing them into our aquariums. And tis is also the reason why we are not fans of dumping the "tea" from botanical preparation into your tanks as a "blackwater tonic" of sorts...Sure, it contains concentrated tannins. It also contains a concentrated "brew" of all of the aforementioned pollutants and undesirable stuff bound up in the dermal layer of the botanicals you just boiled.
Do you really want to add a concentrated "Stew" of this stuff into your closed-stem aquarium? At least when you add prepared leaves and botanicals to your tank, they will release these compounds over time as they break down in the tank, giving your system the time to adjust biologically to handle the gradual release of these compounds.
Okay, I've beaten the shit out of that topic for like the 237th time, so...
And sure, the addition of botanical materials like seed pods and such also has its considerations. The harder-surfaced, more structurally "durable" materials- like seed pods- tend to recruit more biofilms and fungi on their exterior surfaces, which breaking down from the inside- where a greater concentration of lignin and other compounds which make up their interior structure are found.
This is also why you will tend to see less immediate impartation of color into the aquarium when you add stuff like "Sterculia Pods", "Cariniana Pods", "Mocha Pods", "Monkey Pots", etc. It simply takes longer for the exterior tissues to soften and release these substances, whereas the typically softer interior tends to break down faster and impart the compounds present into the aquarium water.
Some of the aforementioned botanicals are, not surprisingly- long-lasting ones when submerged, and will often remain more-or-less structurally intact for many months-or even longer. If you are not a fan of the look of the stringy fungal growths or biofilms on their surfaces, they can be "managed" with a medium-bristled toothbrush.
As far as adding these materials to your tanks- it's largely based on personal aesthetic preference or the goals that you have for your tank. In an unpolluted stem, from "day one" you can knock yourself out and add as many materials as you please. Of course, in an existing, established, populated system that you're looking to incorporate botanicals in, you need to consider them as "bioload", adding to the demands on the bacterial population. You can't simply dump a huge quantity of materials into an established aquarium, which place significant demands on the system's ability to process them.
The result, predictably, would be disastrous.
All additions of botanicals to an existing aquarium needs to be measured, deliberate, slow, and considerate. You need to observe your fishes' reactions, monitor water chemistry, and stay alert to the changes and demands that botanicals will place on your aquarium. And they will. There's no mystery here. Adding a ton of stuff into any established aquarium creates environmental changes and impacts that cannot be ignored.
Those are the environmental considerations of utilizing botanicals in the aquarium. Of course, the aesthetic implications are interrelated to some extent, but have enough unique attributes that we need to think about.
So, from an aquascaping standpoint- leaves should be considered the most "temporary" items we utilizing in our botanical-style tanks, requiring replacement or removal as desired. Those seed pods and stems tend to last longer, and again, it's personal preference to leave them in or remove as desired.
I personally like to leave all of these materials in the aquarium until they completely break down, which, in my opinion, looks interesting, facilitates greater biological diversity, and tends to NOT pollute the aquarium if it's otherwise well managed (ie; if you conduct regular water exchanges, filter media replacements, feed carefully, and stock sensibly, etc.).
I think that we need to look beyond the simple "look" of the leaves and other botanicals in our tanks, and consider them more than just hardscape "props"; rather, they are functional materials, which perform biological, environmental, and physical/structural roles in the aquarium- just as they do in Nature.
So, yeah- there is a lot to consider when utilizing botanical materials in your aquarium. It's far, far beyond the idea of "dump and pray" that has been an unfortunate "model" for how to utilize them in our aquariums for many years. I hope that this generalized, brief, almost "introductory" discussion spurs you to do more research on this interesting and seminal topic in our specialized sector of the aquarium hobby.
Yeah, that's the breakdown on the stuff that..breaks down.
Until Next Time...
Stay informed. Stay curious. Stay observant. Stay diligent. Stay engaged...
And Stay Wet.