Brown oak leaves and a large dried Indian almond leaf resting on sand at the bottom of a freshwater aquarium with tea-tinted water

Tank Care

Fall Leaves in the Aquarium: Indian Almond, Oak, and What's Safe

Which leaves are safe in a fish tank, how many to use, how to collect and prep oak leaves, and which trees to skip.

Jack·8 min read·October 6, 2026

You can use Indian almond (catappa) leaves and dried, brown oak leaves in a freshwater aquarium. Both release tannins that tint the water tea-colored and can pull the pH down a little. They also grow a film that shrimp and snails graze on. Leave out black walnut, butternut and cherry leaves, and anything picked green off a tree, sprayed, or gathered along a road.

The rest of this covers how many leaves to use, how to prep oak leaves you rake up this fall, and what to watch for in a river tank where the current wants to throw leaves around.

What leaves actually do in the water

A dead leaf in water slowly breaks down. As it goes, it lets out tannins and other organic compounds. Those stain the water yellow to amber and gradually lower the pH.

As the surface softens, bacteria and fungi coat it in a thin film. Shrimp, snails and baby fish pick at that film all day. A layer of leaves also gives shy fish a place to hide and gives some species a place to spawn.

The tea color does no harm. Tannins are harmless to fish and shrimp, and plenty of keepers add leaves just to get that look. If you don't like the stain, see the section on clearing it below.

Indian almond (catappa) leaves

These come from Terminalia catappa, a tropical tree. You won't find them on the ground in most of the US, so you buy them dried. A 10-pack typically runs about $7 to $11 as of October 2026, depending on the brand and leaf size.

How many to use: Aquarium Co-op suggests 1 leaf about 4 to 7 inches long for every 5 to 20 gallons. For a 55-gallon, that works out to roughly 3 to 10 leaves. Start low. You can always add more next week.

How long they last: about one to two months before they fall apart completely. You can leave the broken-down pieces in for the shrimp to finish, or pull them when they turn to mush.

Prep: store-bought leaves are dried and cleaned already, so most people just rinse them and drop them in. Boiling dumps most of the tannins out at once, so skip it unless you're trying to keep the color down.

They're often sold with "antibacterial" claims. There is lab work showing catappa tannins have antibacterial activity. Use them to support a tank, but don't count on them to cure a sick fish.

Oak leaves from your own yard

Oak leaves are the free, local version, and fall is when you collect them. Tannin Aquatics, a company that sells botanicals for aquariums, recommends only dried, naturally fallen leaves. By the time a deciduous leaf drops on its own, it has given up most of its chlorophyll and sugars, so it rots slowly and cleanly. A green leaf pulled off the branch rots fast and fouls the water.

What to pick up:

Brown, dry, whole leaves that crunch a little. Skip any that are black, slimy, or moldy.
From a clean spot. Stay away from roadsides and lawns treated with pesticides or herbicides. If you don't know whether a yard has been sprayed, collect somewhere else.
From a tree you've identified. Oak leaves are easy to spot by their lobes, and you can confirm with the acorns underneath. If you aren't sure what tree it is, leave the leaf on the ground.

Oak leaves are tougher than catappa. They break down more slowly, often over several weeks to a few months, so they work well in the back corners of a tank where you aren't vacuuming every week.

Prepping oak leaves

Keepers prep leaves anywhere from barely at all to boiling them. Here's a middle path:

Rinse each leaf under the tap and rub off dirt, bugs and bird droppings.
Pour boiling water over them, or simmer them for 10 to 15 minutes. This kills hitchhikers and helps the leaves soak up water so they sink. Simmering also pulls out some tannin, so the leaves won't stain the tank as hard.
Let them cool. Then set them in the tank, or weigh them down with a rock until they stay under.
Store the rest dry in a paper bag. Plastic traps moisture and they'll mold.

Pick up a bagful now, while the leaves are dry and fresh off the tree. Leaves that sit under snow all winter are past their best by spring.

Other leaves keepers use

Oak and catappa are the common ones. Lists of leaves that are usually considered safe also include beech, alder, hazel, hornbeam, apple and guava. The same rules apply: dried, fallen, unsprayed, and from a tree you've identified.

Leaves to keep out

Black walnut and butternut. Both produce juglone, a compound that is found in their leaves, husks, roots and bark and kills other plants. Pond guides also flag walnut, hickory and pecan. These trees drop leaves at the same time oaks do, so check what you rake up.
Cherry. Pond guides list all parts of cherry trees as toxic to fish.
Anything green, moldy, sprayed or from a roadside.
Any leaf you can't name. When you're unsure, buy catappa leaves for $10 and skip the guesswork.

Leaves in a river tank

A river tank pushes a lot of water, and loose leaves end up wherever the flow drops them. Usually that's against the intake sponge or in one corner.

Put leaves in the slow spots, like behind rock piles or at the outflow end of a river manifold tank.
Pin them down with a flat stone until they're waterlogged. Dry leaves can float for a day or more.
Check the intake sponge more often for the first couple of weeks.
In a riparium, the shallow areas and the land edge are good places to let a few leaves pile up. Crabs, shrimp and snails will work through them.

Critters that use leaf litter well include ghost shrimp, nerite snails and mystery snails. Fish that feed off the bottom will poke through it too. Leaves also work in unheated tanks with fish like White Cloud Mountain minnows. The leaves just break down more slowly in cold water.

When leaves cause trouble

Leaves are rotting organic matter, so too many at once loads up the tank. A water-quality study using Indian almond leaves found that as the dose went up, pH dropped while oxygen demand and bacteria counts rose. Other research on catappa extract found high doses raised ammonia.

In practice that means:

Add leaves a few at a time, not a whole bag. Test for ammonia and nitrite the first week (how to read your kit).
Skip leaves in a tank that's still cycling. Wait until it has finished cycling.
Watch the pH if your fish want hard water. Aquarium Co-op advises against using catappa with high-pH fish like African cichlids and many livebearers. If your tap water is hard, a few leaves won't move the pH much. In soft water, they can move it further. Test it rather than guess, and see adjusting pH in a riparium.
If fish start gasping at the surface, pull some leaves and do a water change, then work through the sudden-loss checklist.

If you don't want tea-colored water

Some people want the leaf benefits without the brown water. Activated carbon in the filter adsorbs tannins, but it gets used up and needs replacing every few weeks. Seachem Purigen also pulls tannins and can be regenerated and reused. Regular water changes dilute the color too. Boiling oak leaves before they go in cuts the stain at the source. The same idea applies to wood, covered in preparing driftwood.

Before you rake this weekend

Pick up brown, dry oak leaves from an unsprayed yard, away from the road.
Look up at the tree. If it's walnut, butternut, hickory, pecan or cherry, leave the leaves where they are.
Rinse, scald or simmer, then pin each leaf down with a stone.
Start with 1 leaf per 5 to 20 gallons, then test ammonia and pH a week later.
Store the extras dry in a paper bag for the rest of the winter.

Sources (6)

Photo by FilipFilipovic on Pixabay.