So we talk a ton about how cool, useful, and desirable it is to have leaf litter in your aquarium, don't we?
Well, I think our enthusiasm stems from the fact that when properly and aesthetically employed, leaf litter adds a new dimension to a biotope-inspired aquarium, and adds a functionality that cannot be denied. Blackwater rivers and streams are characterized by large quantities of leaf litter and decaying botanicals on the bottom, with typically clear (but tinted) water. As discussed many times in this column, leaf litter is used as shelter, spawning ground, feeding area, and in some instances, as supplemental food itself. This is a highly productive habitat in nature that also just happens to look really cool in our aquariums, performing exactly the same function!
In wild habitats, there have been many instances where researchers have counted literally hundreds of fishes per square foot inhabiting the matrix of botanical materials on the bottom of stream beds, which consists primarily of leaf litter. As dead leaves are broken down by bacterial and fungal action, they develop biofilms and associated populations of microorganisms ("infusoria", etc.) that are an ideal food source for larval fishes. When you take into account that blackwater environments typically have relatively small populations of planktonic organisms that fish can consume, it makes sense that the productive leaf litter zones are so attractive to fishes!
Obviously, as leaves break down, the look of your aquascape will "evolve", literally "morphing" into a different scene over time. Consider leaf litter a "transitional" or "consumable" product that needs replacing over time. One of the most common questions we get is how often you need to replace your leaves. Here's my take on the subject:
You don't have to remove the decomposing leaf litter, unless you simply don't like the look. Part of the "charm", if you will, of leaf litter is that it is a surprisingly dynamic environment to watch. However, there are situations where leaving the material in could be detrimental: If it's creating unsanitary conditions, such as trapping excessive amounts of uneaten food, fish waste, etc,degrading water quality- then you'd want to a)review your husbandry practices and b)consider siphoning some of the material out. For most of us, however, I'd say to just leave the stuff in, and add new leaves as needed to maintain the "density" and aesthetic you want.
Preparation is another important part of incorporating leaf litter in your system. There are differing viewpoints on whether or not you should boil or steep the leaves. I definitely would not boil the leaves, because I feel it will remove much of the beneficial tannins and humic substances from the leaves right away. However, I take a very conservative approach in my recommendation to customers and fellow hobbyists: I say that it's never a bad idea to rinse, steep, and soak leaves before placing in your tank.
My main concern about leaves you collect yourself is contaminants, pesticides, etc., so anything you can do to eliminate them is important. They should be dried, of course, before you incorporate them. Don't skip the prep! The leaves I sell are pesticide free and free of major pollutants, yet still should be rinsed at the very least before use. I like the idea of steeping leaves in boiling water for 10-20 minutes, which helps soften them up a bit and "sterilizes" them to some extent, without "cracking off" all of the beneficial tannins bound up in their tissues.
My personal practice is much more liberal: I'll give the leaves a good rinse and typically let them soak a day or two to waterlog them before adding them into my aquariums. Really, the only reason I don't add leaves to my tanks straight away after rinsing is that, with the possible exception of "nano-sized" Catappa leaves, most of them don't sink immmediately!
So, how long do your leaves last? Well, it depends on so many factors, ranging from water chemistry to how "rough" your fishes are with them! Typically, a Catappa leaf will last a month or so before it really starts to break down. Guava, on the other hand, tends to last a much longer time in my personal experience, sometimes 2-3 months or more. Loquat lasts even longer in many cases; I've had some with me for 6 months or more! Others, like oak, beech, Magnolia, etc. are variable.
How dark will your water become as a result of adding leaves? Again, no real one answer- it's a function of many factors combined. In general, I'd suggest starting slowly, particularly if you have very soft water, which can result in significant pH dips rather rapidly when you add a large quantity of leaves at once. An important note: Leaves will not soften hard water. This is a common misnomer. Remember, just because they are staining the water with tannins doesn't necessarily mean that they are softening, or even acidifying, the water to any measurable extent.
They will possibly impact the pH in harder water, but not nearly to the extent that they will in soft water, which is devoid of most buffering capacity/mineral content. It might be argued that a "hard water/blackwater-aesthetic" style system is easier to manage (from a chemical standpoint, at least) than a soft water blackwater aquarium. I'd go so far as to say that a soft water blackwater aquarium with leaf litter and botanicals is on par with a reef aquarium, in terms of the need to manage and care for it. No more difficult than that- it just requires you to be on top of things.
The important takeaway from this brief and highly cursory discussion on leaves is that you should consider them as both a functional and aesthetic component of a well-managed biotope-inspired aquarium for many fishes. The look, the characteristics, and the utility of leaf litter makes it well-worth considering for anyone who is contemplating keeping Characins, Dwarf Cichlids, Catfishes, Barbs, Anabantoids, and many other species of fishes which hail from "blackwater" environments.
I hope you'll learn not to be afraid of the dark (water), and perhaps play around with some leaves in one of your aquariums!
Stay adventurous. Stay focused. Stay engaged.