One of the most common questions we get here at Tannin is "How often do you change out leaves and other botanicals in your aquarium?"
That's actually a tough one to answer, because there is no set timeline or "rule of thumb" to follow for botanical replacement. Leaves tend to decompose much, much more quickly than all but the most delicate botanicals, so if you're up to replacing stuff, it's going to be the leaves typically.
As we've discussed many times here, leaves decompose at different rates, based on numerous factors. There really is no harm in leaving them in the tank to disintegrate completely, in our experience. Indeed, the argument could easily be made that, other than maybe a bit aesthetically displeasing to some, there is no negative to leaving them in.
In our experience, the longest-lasting leaves tend to be Magnolia, followed by Jackfruit, Mangrove (in the brackish aquarium), Guava, Loquat, and Catappa. Keep in mind that the longer-lasting leaves also tend to "recruit" more biofilms over time than the more "ephemeral" catappa leaves.
Regardless of what leaves you favor, they'll eventually start to break down after being submerged for some period of time. That being said, I tend to siphon out the debris when they start "getting in the way" of stuff- you know, blowing into plants or wood or what not, providing more of a distraction than anything else. With the deepl leaf litter beds that some of you are experimenting with, this is again something you'll just have to make the call on for yourself...
I am alos a fan of regularly replacing, or at least adding- new leaves on a continuing basis, as it provides a constant aesthetic "boost", and from a functional standpoint, and sort of mimics what happens in nature, where new leaves are deposited into the water and others are dispersed by currents. Yeah, I can make that case, but the main reason I replace them is because it looks cool and provides a constant "aesthetic refresh!"
As far as pods and other botanicals are concerned, the same philosophy applies. You can leave them in until they disintegrate to little bits, which could literally take years in some instances. Most will break down significantly after a few months. Again, it's more of an aesthetic thing than anything else, IMHO. When they don't look the way you want them to, or don't provide the effect or functionality you want- remove them, or add new ones, at the very least.
The main takeaway here from this brief look at "replacement" is to remember that the most important thing in the maintenance of a closed system aquarium is to minimize environmental fluctuations as much as possible.
By employing regular evaluations and routine "nutrient export" sessions (ie' water changes), you'll create a very stable, surprisingly easy to manage, and undeniably attractive system for your blackwater-loving fishes, blurring the lines between nature and the aquarium.
And, as we have more and more hobbyists playing with these types of systems, more and more refined techniques and ideas will emerge...and we hope that everyone shares their tricks, tips, and discoveries with the ever-growing global community of "tint fans!"
Stay observant. Stay alert. Stay creative.
And stay wet!