I was having a discussion with a customer a few days back, and we were talking about how long some of these aquatic botanicals will last in the aquarium environment. It's a good question, and a great topic for discussion!
Almost the minute you submerge an aquatic botanical, it begins to break down. Like anything else in aqueous environment, seed pods, leaves, and even wood are affected by constant exposure- and the speed of the breakdown and the amount of materials released into the water is dependent upon a variety of factors, including temperature, pH, and water movement, among others.
This release of organic materials from aquatic botanicals is natural and normal, yet it's also why we constantly admonish you to properly prepare them before use, and to go slowly when adding botanicals to an established system for the first time, so as not to overwhelm your tank with a burst of organics and bacteria, which can compete for oxygen with your fishes. And of course, rapidly changing a stable environment through any means is not a good thing for your animals, so common sense should prevail when experimenting with aquatic botanicals. We always recommend that you keep a supply of activated carbon on hand to help remove some of these substances should you find your system being overwhelmed if you "push it" to far to quickly and put your animals into distress.
Tannins and humic acids are released into the water as the cell walls break down, along with other organics. Often times, a "biofilm" of bacteria will form on the surfaces of a botanical after it's submerged for some period of time. In the case of materials like seed pods, the thick outer layers last a pretty long time, while the softer, inner layers tend to decompose more quickly, fostering bacteria and other microfauna in their structure.
It's long been known that "blackwater" seem to have a lower count of dissolved heavy metals, and the humic and tannic acids released into the water column appear to have some anti parasitic/antibacterial properties, in terms of fish diseases. This is obviously a great advantage for fishes that hail from blackwater environments, such as The Amazon and Southeast Asia. For years, better and Discus breeders have exploited this by utilizing Catappa leaves in their systems. It's thought that fishes recover from fin damage, skin lesions, and other maladies more quickly in this environment with a lower parasite count. Studies of wild blackwater systems appear to corroborate this with lower protozoa, insect, and micro invertebrate counts per square meter than other aquatic systems.
Having a mix of materials in your system assures that you'll have a continuous presence of botanicals, releasing some tannins, as well as fostering the development of biofilms and bacteria, which are a food source for many other animals, including fishes and ornamental shrimp, which graze on both the biofilms and the other life forms which subsist on them.
A leaf litter layer in an aquarium performs a variety of functions, including aesthetic, biological, and chemical affects. A blackwater biotope aquarium with a diverse assemblage of botanical materials performs much in the same ways as a "refugium" does in a reef aquarium environment, providing a haven for many life forms and processes, which impacting the display aquarium by providing biological support/diversity, supplemental food production, and chemical enrichment. Blackwater is also known to reduce the amount of micro algae in an aquarium, as a result of the chemical properties imparted into the water, reduced nitrates and phosphates, as well as the brownish tint, which serves as a natural "light diffuser."
Getting back to the first question- just how long do these materials last in the aquarium?
Well, the short answer is "It depends."
It is a function of the aforementioned aquarium environment. In my experience, the materials will last slightly longer in aquariums with higher pH (7.4 and above) than they will in a more acidic environment (like 5.5-6.0). The "sweet spot", in my experience, is around 6.5-6.8, which seems to provide optimum benefits (cleaner environment, low nuisance algae growth, and healthier, more colorful fishes). In this type of environment, it's not uncommon for the more "durable" pods that we offer, such as "Jungle Pods", "Savu Pods", "Tapete Pods","Encontro Pods", etc. to last up to 6-9 months before they break down significantly, although they will begin to degrade substantially in most cases around 4 months.
The less "durable" botanicals, such as Catappa, Guava, and Oak, tend to break down more quickly, becoming essentially inert (from a tannin standpoint) after anywhere from 3 weeks to a month after being added to the aquarium. We've found that the more brittle, yet durable Guava leaves tend to last just a bit longer, although they seem to be an irresistible treat for many shrimp! In general, as leaves break down, fishes such as Plecostomus, as well as a large variety of ornamental shrimp will tend to consume them.
Therefore, it's important to look at aquatic botanicals as "consumable" items, which need to be replaced/replenished from time to time. It's all part of creating a dynamic environment, and is actually analogous to what happens in nature: New fallen leaves and other materials enter the water on a continuous basis as a result of leaf fall, wind, storm activity, etc, an continuously enrich the aquatic environment. This is easily simulated in the closed aquarium environment by replacing these items on a regular basis.
Part of the reason we offer our "variety packs" of botanicals is to give you the opportunity to incorporate a number of carefully selected materials into your blackwater biotope aquarium, while creating a noticeable chemical, biological, and aesthetic impact on your aquatic environment over a period of time. Some will last much, much longer than others, yielding chemical and biological benefits before ultimately becoming more inert. Others, such as leaves, will break down more quickly. Like anything else in the aquatic environment, it will take a little experimenting on your part to find the correct mix of materials that work for your aquarium inhabitants.
We're sure that after some experience, you'll see for yourself the noticeable positive impact that using aquatic botanicals can have on your fishes, with better color, health, natural behavior, and spawning being influenced as a result! The use of these beautiful and interesting natural materials is slowly becoming more widespread in the aquarium hobby as the manyfold benefits become known to aquarists worldwide. We welcome your feedback and observations as you experiment for yourself with the growing array of aquatic botanicals we offer for aquarium use.
Go slowly, observe carefully...
And stay wet.