Have you ever seen a stack of large, dried leaves at the fish store and wondered what they are for? Indian almond leaves (IAL) or catappa leaves come from Terminalia catappa, a tree that originates from Asia and Oceania but now grows in tropical and subtropical regions all over the world. Its fruit seeds taste similar to almonds, and its leaves are commonly used in herbal teas and traditional medicines.
Fruit and leaves of the Indian almond tree
When you drop a dried catappa leaf into your aquarium water, the leaf begins to slowly decompose and produce tannins, which are plant-based compounds that gradually lower the pH and stain the water with a yellow-brown tint. Many people do not like the tannins naturally produced by leaves and driftwood and use chemical filtration to get rid of the brown tint, but they actually have many uses in the fishkeeping hobby.
What are Catappa Leaves Used For?
If you have sensitive species (like crystal shrimp and certain South American fish) that prefer low pH and soft water, Indian almond leaves can slowly lower pH by releasing tannic acid, humic acids, fulvic acids, and other organic compounds with weak acidity. They take longer to work than pH buffer chemicals, but their gradual effect is sometimes considered “safer” because they are less likely to cause deadly pH swings. Because of their impact on water chemistry, the leaves are generally not used for high pH fish like African cichlids and many livebearers.
While some soft water fish don’t require low pH for their normal living conditions, you may be more successful with breeding and raising their fry if you make the water more acidic. That is why breeders often use catappa leaves with their Apistogramma cichilds and betta fish (both Betta splendens and wild type bettas). Also, since the leaves float for the first few days, betta fish and gouramis sometimes create bubble nests underneath them for additional support.
Betta fish in an aquarium with tannin-tinted water
Interestingly, Indian almond leaves are known to have very slight antibacterial and antifungal properties. In nature, tannins help to protect plants from attacks by bacteria, fungus, and other pathogens, and scientists continue to research their antimicrobial efficacy for possible use in human medicine. Therefore, many aquarists like to use catappa leaves to heal mild ailments and aid their fish’s immune systems. For example, if you have a betta fish that constantly bites his own tail, adding tannins may help speed up his recovery and prevent fin rot from setting in. Some veterans also recommend adding tannin-rich leaves or alder cones when hatching fish eggs to fight off fungal growth.
As the Indian almond leaf soaks in water, microorganisms begin to consume and break it down. They rapidly reproduce and grow into a layer of biofilm and infusoria. This microfauna is an excellent food for tiny fry and shrimp and is sometimes the only thing small enough for them to consume during their earliest stages of life. If you plan on going out of town and have no one to feed your shrimp colony, try soaking several leaves in a bucket of water for three weeks until they become very slimy with biofilm. Then drop them in your aquarium as a long-lasting vacation food while you’re gone.
Blackwater biotope aquarium that imitates a Brazilian forest stream
Finally, if you want to create a South American biotype or blackwater aquarium that simulates your fish’s natural environment, use lots of catappa leaves and other botanicals to cover the ground. The darker water makes shiny fish like neon tetras, cardinal tetras, and certain discus really stand out. It also helps skittish fish feel more comfortable since they are more hidden from view by the tannins in the tank. If you add enough Indian almond leaves, the leaf litter can serve as hiding spots for fry or shy bottom dwellers like pygmy corydoras.
How to Use Indian Almond Leaves
If the dried leaves are very dusty or dirty, you can gently rinse them in water first, but the catappa leaves sold by Aquarium Co-Op are clean enough that we just drop them directly into the fish tank. They usually float for the first 3-7 days, so if it bothers you, weigh them down with a rock or decoration. Also, you can break the leaf in half to just use part of it or crumble it into smaller pieces to speed up the decomposition process.
Dried catappa leaves, ready for use in aquariums
How many catappa leaves should I use? Start with 1 leaf (approximately 4-7 inches or 10-18 cm long) for every 5-20 gallons of water. If you are making a blackwater tank, use more leaves and soft woods (like Malaysian driftwood and cholla wood) until you achieve the desired color.
Should I boil Indian almond leaves? We do not boil them because it releases all the tannins and then you don’t get their benefits. However, if you don’t like the way the leaves look, some people like to make a catappa leaf extract by boiling one leaf for every 0.5 gallon (2 liters) of water. (Make sure to use a cheap pot you don’t care about because it may become stained.) Once the liquid has cooled, pour a little into the tank until you reach the color you want. If you add too much extract, just do a water change to dilute the tint.
When should I replace the catappa leaves? Most leaves last about one to two months until they break down completely. Once you start seeing holes develop in the first leaf, add a second leaf to give it time to start breaking down and releasing tannins.
Caridina cantonensis shrimp nibbling on the remains of a catappa leaf
Next time you’re thinking of keeping shrimp, breeding soft water fish, or building a blackwater biotope, grab a stack of catappa leaves to get the job done. Aquarium Co-Op leaves are precleaned and ready to use right out of the package.