Oak in Fish Tank: Curing Process, Pros, Cons

Oak is a fairly common tree in the northern hemisphere. Its gnarly twists and hardiness make many budding aquarists wonder how well it would sit in their fish tanks.

Oaks are among the hardest trees in the world (not in the Top 10 but ranking fairly highly all the same) and that’s important if you consider adding a DYI piece of driftwood to your tank.

So, is it OK to put oak in a fish tank?

Given the proper treatment, oak branches make excellent driftwood decorations. Indeed, they are picturesque additions that provide a strong natural look and a handful of water chemistry benefits.

But before placing any wood you found in the forest in the aquarium, you must cure it properly.

To ensure the safety of your fish, you must follow these steps:

1. Scrub the piece of oak clean of bark and other visible debris
2. Disinfect it, preferably by boiling
3. Soak it in water for 1-4 weeks

Let’s discuss in detail how to prepare the oak, what benefits it brings, and some minor drawbacks it adds.

How to Prepare Oak for an Aquarium

Preparing oak for a fish tank is a fairly straightforward process that requires a bit of manual labor and some patience.

But first, you must examine the piece of oak that had drawn your attention. Make sure that is not rotting, as an already rotting driftwood would dissolve quickly in the tank, making everything messy.

If the oak piece that had piqued your fancy passes this preliminary examination, you can start curing it for your fish tank in earnest.

1. Mechanical Cleaning — Scrub the Oak Clean

Before commencing a proper wood cleaning operation, examine the piece of oak carefully for any overly sharp edges or protruding splinters. If there are any, remove them carefully with sandpaper. The future driftwood must be smooth and safe for both fish and fishkeeper and sharp edges and spikes are dangerous. They can tear fish bodies and fins and are nasty, unwanted intruders into any finger.

Once the wood is safe to work with, start clearing it off in earnest. Remove any bark, mold, and other organics. Technically, you could keep the bark, but it is likely to get loose in the curing process or after you’ve placed it in the tank.

Use sandpaper or a hard brush to clean it well. Take your time and don’t be shy if inspiration hits and you want to sculpt something onto the tree.

If the oak piece has holes, hollows, nooks, and crannies that are hard to reach, use a hard toothbrush. Alternatively, wrap a bit of sandpaper on a metal rod or a pen and go in. Scrub as much as you can.

Don’t use bleach as it may be absorbed by the wood and poison your fish. That’s highly unlikely if you follow my process until the end but better be safe than sorry. 

The next step of the process will take care of anything you might have missed with the mechanical cleaning.

2. Disinfect the Oak

Disinfecting any piece of wood found outdoors is essential to keep your fish safe. Depending on the method used, it may speed up the curing process too.

Here are my three preferred ways of doing it. They are listed in order of preference. I must add the caveat that boiling is quite essential to the entire curing process and would strongly advise to not foregoing it.

1. Boil the Oak

The easiest way to disinfect an oak branch is to boil it in hot water. A good 3-4 hours of boiling will kill anything harmful that might have escaped the attention of your brush. You can add salt to the water, for extra purification impact.

If the log you’ve found is particularly hard and large, boil it longer.

Indeed, the only problem with boiling is size. Driftwood can be bigger than your largest cooking pot. If you can submerge half of it, then rotation is a solution, but if not, the next two approaches will do.

Before we move on to them, I’ll recommend once again boiling the oak. Boiling water opens up the wood and helps massively with the curing process (or waterlogging), on top of disinfecting the wood very easily and reliably. While not as efficient as a few hours of boiling, bathing the oak in boiled water, fresh off the stove also helps. Put it in a large enough container and pour the boiling water.

Repeat this a few times to help the curing process big time.

Soaking it for 48 hours (or more) in baking soda is a solution for larger pieces of wood. The soda will cure the log as well, extracting most of its surface tannins, making it less likely to discolor the water of your tank.

2. Soak in Salt and Vinegar

If you can’t boil the oak piece, grab a large basin or fill up your bath tube with water and submerge the piece of wood. Add a gentle serving of sea or rock salt and wine vinegar and let the wood soak for a week or more. The acidic vinegar and the salt will eliminate bacteria.

Keep in mind that the water will turn brown or black. The tannins released by the oak will change its color. More on that in the last step of the process, once disinfection is complete.

3. Soak in Potassium Permanganate

Potassium permanganate is a strong chemical disinfectant that must be handled with extreme care. Always use protective eyewear and gloves when working with it.

It is dissolvable in water. If you are unable to boil the oak piece, make a 3%-5% potassium permanganate solution in a large vessel and let the wood soak overnight. Once you remove it, wash it thoroughly with running warm water.

If you go this route, better extend the wood curing period to a minimum of three weeks to ensure any trace of the permanganate is gone. In very low doses it won’t damage the inhabitants of your aquarium, but it is best to fully remove it.

3. Cure the Oak

Curing the oak is the last step of the process. Essentially, curing means waterlogging and the process is very simple.

Submerge the oak in water and keep it this way for a couple of weeks or more. In the end, it should lose all its buoyancy. Additionally, the oak will be releasing the majority of its tannins during these baths. I am saying baths because you’ll have to change the water every day or every other day, especially the first couple of weeks.

Toward the end of the first week, the water should stay clearer for longer, but if it’s still getting dark quickly, continue with the process. To speed up the release of tannins, every three days you can scrub the oak with a brush.

When you start getting clear water and the log is no longer floating, you can take the oak piece out, boil it again for a couple of hours (if possible), scrub it one last time, and let it dry out completely.

After a couple of days under the sun, it will be even harder than when you found it and, hopefully, waterlogged enough to stay put at the bottom of your tank.

Benefits of Using Oak Wood in Aquariums

Driftwood has many benefits and oak logs make no exception. In a nutshell, it provides a hiding place for fish and lowers the water’s pH. If you follow the curing process outlined above, the impact on pH won’t be that major, but then again, that depends on the size of your tank compared to the driftwood.

Of course, lowering the pH might not be desirable, depending on the lifeforms in your tank.

It is entirely possible to not soak the oak log for weeks and retain most of its tannins. Then the aquarium water will get darker and the pH will drop more. Some fish will feel right at home in such an environment, but these are specific water conditions and looks that won’t appeal to everyone’s tastes and levels of experience in the hobby.

Speaking of tastes, oak looks great and can add a lot to a classy tank setup.

Drawbacks and Risks of Using Oak Wood in Aquarium

While oak is one of the tree species that are safe for fish tanks, preparing them for their new existence as driftwood is a lengthy process. And even after your best efforts, some issues may occur.

My Oak Log Swims even after Curing

Occasionally, even if the curing process last 4-8 weeks, the oak might refuse to sink. You can tie it to a large stone or even stick it using instant glue.

Sometimes logs refuse to assume their desired spot at the bottom of the tanks, despite our best efforts, so weighing it down remains the only way forth.

Cloudy Water

As mentioned a few times, oaks release tannins that can make the water darker. Usually, this is not a desirable effect. Boiling the oak log in salty water for a couple of hours and scrubbing it will remove a lot of tannins.

If the log continues to muddy your water, soak it in a bucket of water for a few weeks, changing the water daily. Eventually, the polluting effect will diminish and stop.

Risks Associated with Handpicked Oak for Driftwood

Never pick up driftwood close to farms or cultivated fields. That risk isn’t inherent to oak specifically but to any type of wood.

Modern agriculture uses a wide gamma of chemical compounds to fight illnesses and pests. A branch from a tree that grows a few meters away from a cultivated field might be infused with these substances. They are great for putting food on the table, but can be fatal for aquatic animals.

Curing such branches carefully is likely to remove mostly everything, but they are simply not worth the risk.

Take your time and go among nature. Not in a city park. In the forest.

Oak in Fish Tank — the Final Verdict

Oak can make pretty driftwood. Durable and easy to find in some parts of the world, it is an affordable DYI option.

The curing and scrubbing process might sound like a lot, but the hands-on time doesn’t exceed two hours. If the oak log you’ve found is without holes and relatively small, the total involvement will be even shorter than that.

Scrubbing is the most labor-intense part, as boiling and changing water while curing the log is fairly straightforward and undemanding.

Make sure to send pictures of your oak driftwood!