Colin Dunlop discusses the use of dried leaf litter in the aquarium

The use of leaf litter in the aquarium is increasingly popular. © Ryan O’Donnell

For several years I have been using various species of dead leaves in my aquariums. It all started with a large brown leaf that I seen lying on the substrate of a dealer’s tank many years ago.

I was curious about its purpose and the shop staff told me that the fish exporter always packed a few of these leaves in the bags of some of the more sensitive fish. The only information they could provide was that the leaves apparently helped the fish through importation because they contain some sort of medicinal properties.

My curiosity was piqued and I was given a few of the leaves for free because they normally just got binned by the shop. I took them home and added them to one of my own tanks where they gradually disappeared and I never gave them a second thought.

Several years later I recognised the same distinctive leaves on an Internet auction site being sold as ‘Indian Almond Leaves’ and after reading the blurb I thought I would try a few to see if the now extensive claims about the leaves having special properties were true.

After early positive results and more research, I then went on to collecting leaves from local woodlands to experiment with their usefulness for aquariums. After all, I had been using local tree’s roots as decoration for my aquariums, so why not their leaves?

I now make sure that I have dead leaves in every one of my aquariums in which I keep fish from blackwater habitats such as my wild Bettas, Apistogrammas, Badis, wild angels and Uaru fernandezyepeziand with other species too, especially when they have fry.

Beech woods in Cambusnethan, Scotland. Beech is aquarium-safe and easy to collect and use © Colin Dunlop

In my back yard

With my fulltime job as a countryside ranger I visit many different habitats in the local area and I have access to many different species of trees – not all of which are native to Scotland.

So far, I have used leaves from pendunculate oak Quercus robur, sessile oak Q. petraea, Turkey oak Q. cerris, red oak Q. rubra, European beech Fagus sylvatica, hawthorn Crataegus monogyna and Japanese maple Acer palmatum. The cones from European alder Alnus glutinosa have also proven to be worthy of addition.

These trees are just a very small selection of what I could potentially try and hopefully I will have positive results from other species in the future. Obviously I am in Scotland and this is an international website, but the worldwide possibilities would be almost endless so wherever you are at this current moment there should be something nearby of use to you.

However, please extend some caution here before trying “any old leaf” and avoid species that are known to be poisonous.

Leaf litter can be used to replicate the natural habitat of certain fishes, such as Parosphronemus spp. © Gustav Eek

Why bother with leaves?

Chances are that some fish commonly associated with home aquaria, such as discus, would possibly never even encounter an aquatic plant in their whole life in the wild. This is especially true of blackwater habitats where the exceptionally acidic water makes the water mostly unsuitable for plants.

There would be no lush green carpets, no stands of foliage and certainly no sparkly clean water that any bottled-water company would be proud of.

Many of these fish are more likely to be up to their gills in leaf litter and brown-stained water. In fact, it has been said that many fish collectors will not even bother to get their nets wet if there is no leaf litter on the substrate if searching for certain species.

The leaves make up a huge matrix of an aquatic habitat and as many as several hundred Apistogrammai spp. have been recorded per square meter of leaf litter.

The benefits

The crux of the matter really has to do with the tannins which are released from the leaves and this is not a new notion as some companies have been selling blackwater extract for years for use with suitable fish.

Adding dead leaves will have the resulting effect of releasing humic substances and this will lower the pH of the aquarium water, act as an anti-bacterial and anti-fungal agent, and also lower the heavy metal content of the water.

Comparison of water stained by the addition of leaf litter (left) and fresh tap water (right) © Colin Dunlop

It is widely accepted that it acts as a spawning trigger and can aid in the recovery of any fish damaged through stress or fighting. From my own observations and with the backing of some scientific research by the likes of Dr Christian Steinberg, it has been proven that there are many positive reasons why using humic substance releasers, such as dead leaves, are good for the aquarium fish we keep.

One further point that I’d like to stress is that a layer of leaf litter in the aquarium will start to give the water a weak yellowish-brown tinge and this is a good indication of just how much humic substance is in the water. It cannot be tested with an off-the-shelf test kit so it really is best done by the eye. If the water starts to go brown then I usually decide that I have added too much humic substance and cut back a bit.

Some people will actually have a spare bucket filled with water where they add a lot of leaves or alder cones and use this as a concentrated solution. You can then remove water by the jar-full and add this to the blackwater tank until it is the right “colour”. You will find that blackwater fish will do much better and be less shy in tanks where the water has a tannin stain and subdued lighting also helps.

Any other benefits?

Yes, there is more… I had my suspicions that having dead leaves in aquariums was actually acting as a food for some fish, particularly with fry. I was able to witness that fry in tanks with leaf litter seem to grow bigger faster and I could often see the young fish grazing on the leaves.

I had assumed that it was the leaves themselves that were being eaten but while reading the TFH book, “Culturing Live Foods”, Michael Hellweg makes reference to using dead leaves from hardwood trees as a method of feeding larval fish.

Leaf litter may also provide a source of food for the fry of some species, such as this Dekeyseria brachyura © Colin Dunlop

He explains that blackwater habitats are characterized by having large amounts of leaf litter and very low pH and that there are relatively few planktonic animals on which young fish can predate. Some fish species get round this problem by excreting large amounts of slime from their bodies for the fish to eat (discus, uaru etc) and this can sustain the young fish for several weeks.

As dead leaves are broken down by bacterial and fungal action they produce a slime and it would seem that this is what the baby fish are feeding on. I have certainly had high survival rates from loricariid fry where leaves have been present. Lastly on this subject, the leaves also seem to kick-start infusoria populations, again perfect for feeding tiny fry.

Collection of the leaves

The most important issues when it comes to using dead leaves are in their identification, collection and preparation. It is important to only collect leaves that have fallen from the trees and are not fresh living leaves.

During the autumn the deciduous trees start to shut down for the winter and the leaves which have worked as factories all through the spring and summer months producing sugars and oxygen are gradually killed off and fall to the ground. These are the leaves we want to collect as they have no living matter in them that could cause problems in the tank as they die.

If you don’t know your tree species then it might be worth getting a hold of small pocket guide to trees so you can try and get the right species and it makes sense to try and collect the leaves in areas away from roads and any other sources of pollution. You should also try to avoid any that are overly dirty in mud or perhaps covered with bird droppings.

Leaves are best-collected when freshly-fallen in autumn, though care must be taken to identify them correctly © Colin Dunlop

Typically I fill several bin bags with leaves and take them home to dry them out. You might want to dry them out in the garage or a fish shed if you have one because it is quite normal to have stowaway spiders and other minibeasts which you might not appreciate moving into your house.

I collect enough leaves in the autumn to see me through to the next year and store them in a dry environment tied in large fish bags or similar once they are properly dry.

How to use them

Do not boil them in water before use. Yes, you will sterilise them but it will also boil off a lot of the beneficial reasons that we want them for in the first place. I just add them to the aquarium in their dried out state after their correct storage. The leaves will naturally float but most will have sunk within twenty-four hours or so.

There are no rules as to how much to add so it will need some trial and error. Much of this will be influenced by the species of leaf as some contain more tannins than others. For example with beech leaves I could add a few inches of leaves with only a slight staining of the water but more than four or five individual leaves from Indian Almond trees and the water will look like tea!

You do not need to remove the leaves after a period of time as they gradually break down altogether and can be simply replenished by adding more to the tank. Some leaves will last much longer than others and again using my two earlier examples; Indian almond leaves may only last a couple of months whereas beech leaves may take more than six months to break down.

Leaves can be left in the aquarium to break down and will not harm livestock © Colin Dunlop

In closing, at a time when we should all be more environmentally aware and realise that the traditional method of staining water, peat, is a valuable habitat not to be destroyed, that I have found the use of dead leaves to be environmentally friendly, cheap, interesting and overall valuable in the keeping of any fish I have had which would naturally require blackwater, soft, acidic conditions and recommend that you give them a try, perhaps starting with the easy to obtain Indian almond leaves and then move on to some locally found species.

Biography

Hellweg, M. R. 2008. Culturing Live Foods: A Step-by-Step Guide for Culturing One’s Own Food for the Home Aquarium. TFH Pubns Inc. ISBN-10: 0793806550 ISBN-13: 978-0793806553

Steinberg, C. 2003. Ecology of Humic Substances in Freshwaters: Determinants from Geochemistry to Ecological Niches. ISBN-10: 3540439226 ISBN-13: 978-3540439226