Top 5 Botanical Caves for Aquarium Fish

Many of the popular species of fish in the aquarium hobby require some sort of cave or shelter to thrive in our fish tanks. Even species that do not use caves constantly may still seek them out during spawning.

We can provide them this shelter in many ways: repurposed terracotta flower pots, lengths of PVC pipe, purpose built fish caves and ornaments, and sometimes cleverly placed pieces of wood and rocks. All of these are suitable, but some do look better than others in our aquariums. 

However, there is one other option that is growing in popularity: botanicals. This term covers everything from dead oak leaves, exotic palm fronds, tannin-packed alder cones and various seed pods. The latter is the focus for this article, as there are many amazing natural materials found across the world that work perfectly as caves for our fish. 

Using Seed Pods in Aquariums

Adding dead organic matter to an aquarium in the form of botanicals seems scary at first – I know it did to me initially. However, these materials fall into bodies of water all over the world, and when done correctly it is perfectly safe and often very beneficial to our fish. 

Many botanicals will leach tannins once submerged, and the exact amount varies greatly. This not only looks natural and helps fish feel more secure, it also lowers pH in water with low carbonate hardness and helps to recreate blackwater conditions in the aquarium. 

As with any botanical, or aquarium wood for that matter, seed pods need some preparation before use. They are a natural, terrestrial material that will likely float when added to water, and they can have pollutants, dust, and debris on their surfaces. 

A simple preparation process helps waterlog the pods and removes debris before they are added to the aquarium. 

How to Prepare Botanicals Safely

1. Rinse them with tapwater to remove any dust that may have accumulated.

While this dust and debris isn't likely to be harmful, it may cause your aquarium water to go cloudy. You can just run them under the tap for this, as the chlorine will not cause any issues at this stage. 

2. Add the botanicals to a dedicated sauce pan and bring them to a boil for a minimum of 10 minutes.  

You can split this into two sessions of boiling.

The first can be done with tap water for 5 minutes before straining. This helps to remove more stubborn surface contaminants, opens up the tissues of the botanicals, and removes any excess sugars that could impact the water parameters. 

You can then use dechlorinated tap water, or RO water, for the second boil meaning the resulting tannin stained water can be used as a blackwater extract. You can prolong this second boil for as long as you like, until the materials are no longer buoyant. Larger seed pods usually contain more air and take longer to become waterlogged whereas leaves will usually sink after 10 minutes. 

3. Leave the seed pods to cool down

This is not only safer for you, but also for your fish tank's inhabitants. If you do not plan to use the blackwater extract produced from boiling you can carefully strain the botanicals at this stage to help speed up the cooling period. 

4. Slowly add the botanicals to your display

Now comes the enjoyable part, placing the natural materials into the aquarium. For established tanks, only add a small number of pods or a few leaves at a time, and wait a week or so before adding more. The tannins that leach from these materials can alter your water parameters and you don't want the pH to drop too quickly.

Also, bacteria and fungi will colonise these newly submerged items and multiply rapidly. Add too many in one go and you may get an ugly bacterial bloom, which uses up a lot of oxygen and can cause issues for your fish. However, in a newly set up aquarium without any livestock you can add as many as you want, you will simply need to wait for the tank to stabilise. 

Fishkeeping Top Tips

You can place the botanicals randomly for a truly natural look, this works great for smaller items and leaf litter. Larger seed pods, including the cave-type ones that are the focus of this article, can be placed more carefully:

• Follow the rule of thirds with large seed pods, this ensures the final display is pleasing to the eye.
• Use an odd number in displays just as you would with rocks in an Iwagumi. This helps to prevent the aquarium looking too symmetrical. If you have three of the same pod, add two on one side, and one on the other. 
• Place caves so that you can see into the opening. This can help you check if your fish have spawned, and allow you to keep an eye on your cryptic pets. 

Best Seed Pods for Cave-Dwelling Fish

Now we know how to use them, which botanicals should you buy for your cave dwellers? Below are our favourite options, with a variety of sizes making them suitable for different species. All of these are quite sturdy botanicals, meaning they are durable and won't decompose quickly, we are talking years rather than months for their life span in aquariums. 

Savu Pod (Cariniana)

This wonderful botanical comes from South America, making it an ideal option for biotope aquariums based on Brazilian blackwater habitats and Colombian flooded forest streams. They are available in a variety of sizes, typically between 5-10cm (2-4") with openings up to about 2cm (0.75"). 

They work great for so many species and I have observed Apistogramma, juvenile Hypancistrus, Betta albimarginata, and various Parosphromenus all utilise them at various times. 

Buddha Nut (Pterygota)

These tropical-looking pods are great for providing a bit of shade for shy species. Indeed, I've even witnessed six banded barbs using these seed pods for cover. However, their wide openings make them less suitable for cave-spawning fish. Like with all botanicals, each piece is unique, and some pods will have wider openings than others. 

The Pterygota alata trees have a wide distribution across Southeast Asia. Their seed pods range in size, but can be as large as 10cm (4") in diameter.

Jungle pods from the genus Sterculia are a similar looking option that are often slightly smaller. 

Ourico Pods (Bertholletia)

This is the outer shell of the Brazil nut, and is an incredibly thick, sturdy, and long-lasting seed pod. Again, this is a seed pod with a wide opening, so wouldn't be ideal for species that like the safety of a narrow entrance, female Apistogramma being a notable example as they regularly build up sand to close up the entrance to their caves. 

Photo by Matt Hayes

Deeper bodied dwarf cichlids, like Bolivian rams, Laetacara and Ivanacara, are likely to enjoy sheltering in an Ourico pod though. Indeed, these have a tendency to spawn on hard surfaces in more open areas, so the inside of these pods may be a great spot for them.  

Equally, you could lay the opening down on the substrate, propping one end up with a small rock to make a dark cave for nocturnal catfishes and shy loaches. 

These are available in a variety of sizes, including chunky 15cm (6") specimens. It's always worth adding a note to any order if you have a specific size in mind, as they may be able to select the perfect pod for you. 

Bertholletia excelsa trees grow in the north and central regions of South America. 

Cacao Pods (Theobroma)

Housing the all important cocoa bean that we all readily consume in one way or another, the seed pod of the Theobroma cacao tree is also useful for aquariums. It has a dark colour, even before being waterlogged, and its hollow structure makes it an ideal cave for a variety of cave-dwelling fish.

Indeed, I have seen plenty of evidence that domestic Bettas also like to use them as a place to rest, especially when they are placed a little higher in the aquarium. 

This is another larger pod, which can reach 18cm (7.1") in length, although the ones I have used have been around the 10cm (4") mark. However, the opening is usually a little more enclosed than the Jungle or Ourico Pods depending on how they were cut. 

Theobroma cacao is native to South America, but it has been introduced in parts of Southeast Asia, Africa and Central America. This means it would be a suitable botanical for a wide range of biotope aquariums. 

Fishkeeping Top Tip

When you purchase one of these pods, the opening will probably have been cut very straight, making it look a little unnatural. Rough up the edge of the pod with some pliers or secateurs for a more natural display. 

Coconut Cave (Cocos)

This might be one that you are already familiar with, as they do pop up in fish stores from time to time, although more regularly for reptiles. While you can buy them already cut in half with a hole, you can just as easily make them yourself. 

The benefit of buying a whole coconut and creating your own cave from it is you can cut the hole to fit the species you are keeping. Remember when I said about female Apistogramma liking a narrow entrance, well now you can provide the perfect size one for her! 

Cheap and durable, but perhaps not as aesthetic as some of the other options, they are so versatile that coconuts had to make it into the top 5 list. The Cocos nucifera tree is native to northeastern Australia, New Guinea, and various Pacific Islands but has been introduced throughout the tropics. 

Botanical Aquariums FAQs

Below are some of the frequently asked questions about using seed pods and leaf litter in fish tanks. 

Can I collect my own botanicals? 

You absolutely can, although finding cave like seed pods here in the UK will certainly be a challenge. You can read more about collecting leaf litter here, and the same principles can be applied to seed pods too. 

I love the idea of natural caves but I don't like the look of brown water, what can I do? 

The tannins that discolour the water can easily be removed by using activated carbon, or a resin like Seachem Purigen, in your filter.

Also, many aquarium soils designed for plants appear to remove tannins from the water over time helping to reduce discolouration, although I would not use these soils solely for this purpose.

Related article: Five ways for you to achieve crystal-clear aquarium water.

There seems to be a lot of contrasting advice on botanical preparation, what's true and what's not? 

Yes, everyone has their own methods, and they all likely work to some extent. Personally, I like the safety of boiling botanicals even if I lose a small amount of tannins because of it and that is why I recommend doing it this way. However, I have sometimes just rinsed off larger palm leaves and seed pods that wouldn't fit in my saucepan. 

My seed pods still float after boiling, what should I do?

This is always frustrating but it is fairly common. Just like with floating wood, we can secure stubbornly buoyant botanicals by wedging them between rocks or gluing them down. Equally, you can just let them float in the tank until they naturally sink. 

If none of these sound like suitable options for you, pick the floating seed pods out of the water and put them back in the saucepan for a bit longer until they sink. 

A Botanical Cave for All

Seed pods and other botanicals are an excellent way to create natural-looking shelters for cave-dwelling fish. Whether you keep Apistogramma, Bettas, catfish or shy loaches, there is a suitable botanical cave for almost every setup. With proper preparation and thoughtful placement, these natural materials can become both practical shelters and striking aquascaping features.

Share photos of your fish enjoying their natural caves on our Readers Tanks page, or email them to us at [email protected]