As we all know, nothing lasts forever.
And it's especially true with our botanicals.
There is a real "pace", a process- a cadence to what occurs when they are utilized in our aquariums.
From the minute you prepare a leaf or botanical for use in the aquarium, it begins to break down.
The processes of hot water steeping, boiling, or prolonged soaking start to soften the tissues of the leaves or seed pods, release bound-up pollutants, and begin the gradual, but irreversible process of breaking down, at a pace, or "cadence" which nature determines.
As botanical materials break down, more and more materials (tannins, humic substances, lignin, bound-up organic matter) begin leaching into the water column in your aquarium, influencing the water chemistry and overall environment. Some, like Catappa leaves, break down within weeks, needing replacement if you wish to maintain the "tint level" you've started to achieve in your aquarium.
Knowing when to replace them is sort of a subjective call, at least initially. Once you get used to working with them in your aquariums, you may be able to notice pH increases, TDS changes, or other environmental/water chem indicators/phenomena which can clue you in that it's time to replace them.
On the other hand, many types of seed pods and other botanicals will last much longer periods of time than leaves in most aquariums, yet may not impart their tannins and other substances as quickly as say, leaves, simply because their very structure is different than the softer, thinner leaves. Many will hold their form for a very long period of time, yet may not be releasing quite as much tannins or humic substances as they were initially.
Again, it's sort of a judgement call.
Without the ability to measure the levels of the specific substances that botanical items are imparting into your tank (and, quite frankly, knowing just what they are!), it's really about "nuancing it", isn't it? Like so many other things in this hobby, you sort of have to take a "best guess", or go with your instincts. Hardly the precise, scientific, "boiler plate" advice some of us might like, but that's the reality of this kind of tank. It's not like, our example, a reef tank, where we have detailed chemical baselines for seawater parameters, and 32-component ICP-OES tests to establish baselines and measure deviations from them.
Nope. It's about nuance, observation, "feel"... finesse.
Obviously, you need to obey all of the common best practices of aquarium management, in terms of nitrogen cycle management, water quality testing, nutrient export, etc. in a botanical-style blackwater aquarium. However, you have to also apply a healthy dose of the above-referenced "emotional elements" into your regimen as well!
Remember, anything you add into an aquarium- wood, sand, botanicals, and of course- livestock- is part of the "bioload", and will impact the function and environment of your aquarium. I
t's about understanding a balance, a quantity, a "cadence" for adding stuff, so that the closed environment of your aquarium can assimilate the new materials, and the bacteria, fungi, and other organisms which serve to break them down can adjust.
Rapid, dramatic environmental shifts are never a good thing for any type of aquarium, and a system like we run, with lots of organic material present, is just as susceptible to insults from big moves as any other- perhaps even more.
Again, the key here is that "cadence"- understanding that the material we add needs to be added-and replaced- on a pace that makes sense for your specific system. Those of us who have been maintaining these types of tanks for some time now really get this, and have a great "feel" for how our tanks run in this fashion.
Again, there is no "plug and play" formula to follow- only procedure. Only recommendations for how to approach things. We sound a bit like the proverbial "broken record"; however, like so many things in aquarium-keeping, our "best practices" are few, simple and need to be repeated until they simply become habit:
1) Prepare all botanicals prior to adding them to your aquarium.
2) Add botanical materials slowly and gradually, assessing the impact on your aquarium environments and inhabitants.
3) Either remove botanical materials as they break down (if that's your aesthetic preference), or replace them when they reach a point where they are no longer providing the aesthetic and environmental conditions that you desire.
4) Observe your aquarium continuously.
If you noticed, the first practice is simply logical.
You need to employ it...if there were ever a "hard and fast rule in the botanical/blackwater game, this would be it. Number 2 is all about the cadence...the real "secret", if you will, which sort of sets up everything else.
BY observing and assessing, you'll get a real feel for how botanicals work in your aquarium. And #3 is the real "finesse" part of the equation...the nuance, the subtle, yet noticeable adjustments and corrections we make to keep things moving along nominally- sort of like pruning in a planted tank, or weeding a garden...it's a process.
In fact, the entire experience of a blackwater, botanical-style aquarium boils down to a process and a pace that helps foster the gradual, yet inexorable "evolution" of the aquarium. And let there be no doubt- a botanical-style aquarium does "evolve" over time, regularly and steadily changing and progressing. As we've mentioned before, it might be the perfect expression of the Japanese concept of "wabi-sabi", popularized by Takashi Amano, which is the acceptance of transience and imperfection.
And it's all held together by you- the aquarist, applying as much emotion as you do procedure- all done in the proper time...at the right cadence.
Stay focused. Stay in touch. Stay attuned. Stay observant...
And Stay Wet.