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You added a beautiful piece of wood and suddenly your aquarium water looks like tea. Don’t panic—this is very common and usually not dangerous. In most cases, the brown tint comes from natural tannins and other organic compounds that leach from new or unprepared driftwood. In this guide, you’ll learn what’s happening, how to tell if it’s harmless or a problem, and several easy ways to clear the water (or embrace the natural “blackwater” look if you like it). Everything here is explained in simple, beginner-friendly English.
The quick answer
When you add wood to an aquarium, tannins and humic acids often leach out. These turn the water brown or amber, similar to brewed tea. This is normal. It is usually safe for fish and plants, and some fish actually prefer it. If you want clear water again, water changes, carbon or Purigen in your filter, and pre-soaking or boiling the wood can help. If the water is brown but also cloudy or smelly, you may have extra debris, a bacterial bloom, or diatoms along with the tannins. The steps below will help you tell the difference and fix it.
What causes brown water after adding wood?
Tannins and humic acids
Wood is full of natural compounds called tannins and humic substances. When the wood sits in water, these slowly dissolve into the tank. They act like a natural dye, staining the water a yellow, amber, or brown color. This “tea stain” can be light or very dark depending on the wood type, how new it is, and your water chemistry. It’s the same reason tea bags color hot water—it’s the same family of compounds, just from wood instead of tea leaves.
Biofilm and the “white fuzz” stage
New wood often develops a white, slimy coating within the first few weeks. This is biofilm, a mix of bacteria and fungus-like organisms that feed on the sugars and dissolved organics in the wood. The biofilm is harmless and temporary. Shrimp, snails, and some fish will eat it. While biofilm itself does not make the water brown, the breakdown of organics can add to the overall tint and can make the water look slightly cloudy if there’s a lot of it floating around.
Diatoms versus tannins: know the difference
Tannins make the water look like tea but still mostly clear when you look through it. If your water looks brown because surfaces are coated in a dusty brown film (especially on glass, leaves, and sand), that’s likely diatoms (brown algae). Diatoms thrive in new tanks and when there are silicates present. They make things look brown even if the water itself is not stained. Wipe a patch of glass—if a brown powder comes off, you’re dealing with diatoms, not tannins.
Mulm and disturbed substrate
Sometimes the water turns brown or murky right after you add wood because you stirred up dirt, wood dust, or substrate mulm. This is not the same as a tannin stain. Mulm makes the water cloudy and dirty-looking. Good mechanical filtration, a quick water change, and time will clear this. If the tint remains as the cloudiness settles, that color is likely from tannins.
Is brown water harmful?
For softwater and blackwater fish
Many popular fish come from blackwater habitats where leaves and wood stain the water naturally. Tetras, rasboras, bettas, gouramis, apistogrammas, and many catfish enjoy tannin-rich water. Tannins have mild antibacterial and antifungal properties and can reduce stress for these fish by dimming the light and mimicking their natural environment. In these cases, the brown tint is a feature, not a bug.
For hardwater fish and shrimp
If you keep fish that prefer hard, alkaline water (like many livebearers—guppies, mollies, platies—or African cichlids), a heavy tannin load may nudge your pH downward. In high-KH water, the pH change is usually small. In low-KH water, pH can drop faster. Shrimp generally do well with tannins, but sudden changes in pH or water chemistry can stress them. As always, stability is key. If your tap water is very soft, use a buffer or crushed coral to prevent big pH swings when adding fresh wood.
Effects on pH, KH, and oxygen
Tannins are weak acids, so they can lower pH slightly. The amount depends on your KH (carbonate hardness). Low KH means pH can shift more; high KH resists change. Tannins do not directly reduce oxygen, but murky water from decaying debris or dirty filters can. Keep good flow and clean your filter if you notice reduced performance. If you have very low KH, monitor pH during the first few weeks after adding wood.
How long will the brown color last?
This depends on the wood type, size, and how you prepared it. Heavily tannic woods like mopani and some bogwoods can leach for weeks or months, fading over time. Lighter woods like manzanita tend to release less. If you pre-soak wood for 1–3 weeks (changing the soak water), much of the initial stain will be removed before the wood touches your aquarium. Without pre-soaking, expect stronger color for the first 2–6 weeks, which then slowly decreases.
How to confirm the cause
Visual checks
Stand back and look through the tank at a white wall or a sheet of paper. Tea-colored but clear water points to tannins. If the water is tea-colored and hazy, you might have both tannins and fine debris. If surfaces are coated in brown dust and the water itself is fairly clear, it’s diatoms. If the water is milky white or gray, that’s likely a bacterial bloom unrelated to tannins.
Water tests to run
Check pH and KH before and after adding wood. A small, gradual pH drop is normal with tannins, especially in low-KH water. Ammonia and nitrite should remain at zero in a cycled tank. If ammonia or nitrite appears, the brown color is not the real problem—you’re seeing a cycle issue or heavy decay. If you run a silicate test and it’s high, diatoms are more likely. Nitrate should rise slowly over time, not spike suddenly. Use your test results to choose the right fix below.
Fix it your way: three approaches
Option A – Embrace the natural blackwater look
Many aquarists love the amber look. It softens lighting, brings out colors in tetras and bettas, and can even reduce some algae. If your fish are appropriate for soft, tannin-rich water and your pH/KH stay stable, you can keep it. Just do your normal water changes and maintenance. You can also add catappa leaves, alder cones, or peat to deepen the color intentionally if that suits your biotope.
Option B – Gentle clear-up (keep a light tint)
If you like a faint tint but want less staining, do smaller but regular water changes (for example, 20–30% weekly), and run a small bag of activated carbon or Purigen in your filter. Replace or recharge it when the tint returns. This approach balances the natural look with more clarity.
Option C – Clear water fast
For a quick return to clear water, combine several actions: remove the wood and pre-soak or boil it, do a series of partial water changes, and run fresh chemical media (carbon or Purigen). Vacuum any loose debris. Within a few days to a couple of weeks, most tanks become noticeably clearer, especially if the wood is reintroduced after soaking.
Step-by-step: removing tannins effectively
Pre-soak or boil new wood
Rinse the wood under running water and scrub off loose dirt. Soak it in a bucket or tub of dechlorinated water. Change the soak water daily or every other day until the water remains mostly clear between changes. This can take 1–3 weeks depending on the wood. Boiling is faster if the piece fits in a pot. Simmer for 1–2 hours, replacing the water as it turns dark. Boiling helps drive tannins out and also waterlogs the wood so it sinks. Do not add soap or chemicals. Let it cool completely before putting it in your tank.
Partial water changes on a schedule
Frequent partial water changes dilute tannins. Try 25–50% every few days at first, then weekly as the color fades. Dechlorinate new water and match temperature to avoid stressing fish. If your pH or KH are low, test during this process to keep parameters steady.
Use targeted filtration media
Activated carbon is simple and cheap. Place a fresh bag in your filter and replace it every 2–4 weeks or when the tint returns. Purigen is a synthetic resin that removes dissolved organics very effectively; it turns brown as it absorbs and can be regenerated with bleach following the product’s instructions outside the tank. Other resins designed for organics work too. Chemical media clear the color but do not solve the source, so pairing them with pre-soaking is best.
Improve mechanical filtration for debris
If the water is brown and cloudy, add extra filter floss or a fine polishing pad to catch small particles. Rinse or replace it as it clogs. Make sure your filter flow is steady and not reduced by clogged media. Vacuum the substrate gently to remove wood dust and mulm.
Light and plants can help
Live plants use dissolved organics and can slightly reduce the load that becomes tint. Fast growers like hornwort, water sprite, or floating plants can help polish water over time. Also, strong light makes a slight tint more noticeable. If you reduce intensity a bit, the tank may look clearer without changing anything else.
Prevent brown water next time
Pick the right wood
Different woods release different amounts of tannins. Mopani and some “bogwood” pieces are heavy leachers. Malaysian driftwood is moderate. Manzanita, spider wood, and cholla often release less, but they can still color water at first. Avoid resinous softwoods (like pine) and random outdoor branches that may carry sap, pesticides, or rot. When in doubt, buy aquarium-safe wood from a trusted source.
Prepare wood before adding it
Always scrub, rinse, and pre-soak new wood. If the piece is small enough, boiling speeds up the process. Soaking until the water stays mostly clear is the best sign it is ready. If the wood floats, weigh it down with rocks or tie it to slate. This also keeps it from rubbing substrate and kicking up mulm.
Avoid common mistakes
Do not use soap, detergents, or household cleaners on wood or inside the tank. Do not try to bleach driftwood to remove tannins. Bleach can damage the wood, harm biofilm balance, and is risky if not perfectly neutralized. Do not panic-clean your entire filter when you see brown water; you might remove too much beneficial bacteria. Tackle the tint gradually and keep your cycle stable.
Special cases and FAQs
The water turned brown months after adding wood. Why now?
A shift in water chemistry can release more tannins later. For example, a lower KH after many water changes or a big pruning of plants can change organic loads. Wood can also release tannins in waves as it continues to break in. Use carbon or Purigen for a while, and the water should clear up again.
It smells earthy. Is that bad?
A mild earthy or “forest” smell is normal with tannins. A sour, rotten, or fishy odor points to decaying organic matter or a filter issue. If the smell is unpleasant, clean out trapped debris, rinse mechanical media in tank water, vacuum the substrate, and check that your filter is flowing well.
Is the brown color safe for shrimp and snails?
Yes, and many shrimp keepers add leaves and wood on purpose. Tannins can help shrimp feel secure, and biofilm on wood is their favorite snack. Just avoid rapid swings in pH or temperature. If you keep very soft water, monitor KH and pH so they don’t crash as the wood leaches.
Will tannins stain aquarium glass or silicone?
No. Tannins do not permanently stain glass or silicone. A normal wipe with a sponge or algae scraper removes any film. If your silicone looks tinted, it’s usually just a thin biofilm that cleans off easily.
My water is brown and my fish are gasping. What should I do?
Tannins alone do not cause gasping. Gasping suggests low oxygen or poor water quality. Increase surface agitation, clean the filter intake and media (in tank water), and test for ammonia and nitrite. Do a partial water change. Once your parameters are safe, you can focus on clearing the tint if you still want to.
Can I use tea bags or peat to create blackwater instead of wood?
Some aquarists use peat or botanicals to create blackwater, but tea bags are not recommended because many contain additives. If you want a controlled blackwater effect, use aquarium-safe botanicals, catappa leaves, or a blackwater extract. Always monitor pH and KH.
The wood keeps floating and stirring up debris. Help!
Pre-soak longer, or boil if possible. You can also screw the wood to a piece of slate and bury the slate under the substrate, or wedge the wood with rocks. Once fully waterlogged, it will sink on its own, usually within a few days to a few weeks.
Is it better to remove the wood to clear the water?
If you want fast results, taking the wood out and pre-soaking or boiling it helps a lot. While the wood is out, run carbon or Purigen and do a couple of water changes. When you put the wood back, the stain will be much lighter or barely noticeable.
Could the brown color be from something else?
Yes, but it’s less common. Peat filtration, leaf litter, and some fertilizers can tint water. Severely decaying organics can also add color and odor. If you just added wood and see a tea-like tint with no bad smell, it’s almost certainly tannins from the wood.
Realistic expectations by wood type
Mopani and bogwood
Often release a lot of tannins at first. Pre-soak or boil if you want clear water. Expect weeks of tint without preparation, fading over time. On the positive side, these woods are dense, sink well, and last a long time.
Malaysian and spider wood
Moderate to light tannin release. Spider wood can grow a dramatic white biofilm in the first month, which is normal and temporary. Pre-soaking helps reduce both tint and biofilm intensity.
Manzanita and cholla
Usually lighter in tannins, so the stain is less intense. These woods are popular for aquascapes that aim for a clearer look, though pre-soaking is still recommended.
If the brown is diatoms, not tannins
How to tell and what to do
Wipe a small area of the glass; if a brown powder comes off, that’s diatoms. They are common in new tanks and when silicates are present (from new sand, tap water, or certain rocks). To fix diatoms, keep up with water changes, use good light duration (6–8 hours at first for new tanks), add a small cleanup crew like nerite snails or otocinclus in mature tanks, and wait. Diatoms usually fade on their own as the tank matures.
Balancing looks and fish health
Choosing your finish
There is no single “right” water color. Clear water shows off aquascapes and bright fish. Amber water creates a natural, calm mood and suits blackwater species. Your fish’s needs and your taste both matter. You can aim for clear, slightly tinted, or dark tea—just keep water quality stable and let your fish tell you how they feel through their behavior and appetite.
A simple action plan
For a new tank with fresh wood
Test pH and KH. If they are stable, wait a week to see if the tint settles. If you dislike the color, add carbon or Purigen and do one or two 30–50% water changes. If still too dark, remove the wood to pre-soak or boil, then reintroduce it.
For an established tank that just turned brown
Check for debris and clean mechanical media. Vacuum the substrate lightly. If the tint is from tannins and there is no smell or cloudiness, use chemical media and a few partial water changes. If you detect ammonia or nitrite, address the cycle and filtration first.
Common myths to ignore
“Brown water is dirty or unsafe.”
Not true by default. Brown from tannins can be healthy and natural. Dirty water is cloudy, smelly, or shows bad test results.
“You must replace your filter right away.”
Changing all filter media at once can crash your cycle. Only add or replace carbon/Purigen. Rinse sponges in tank water but keep your beneficial bacteria intact.
“A full water change is the only fix.”
Large, sudden changes can stress fish. Several partial changes are safer and just as effective over a short time.
Conclusion
Brown water after adding wood almost always means tannins are leaching into your aquarium. This is a normal, natural process. For many fish, it’s a benefit, not a problem. If you like the look, enjoy it. If you prefer clear water, you can reduce the color with pre-soaking or boiling the wood, steady partial water changes, and a small bag of carbon or Purigen in your filter. Make sure you can tell tannins from other causes like diatoms or debris so you use the right fix. Keep an eye on pH and KH in soft water, and aim for stable, clean conditions rather than chasing a perfect color in one day. With a little patience and the steps above, you’ll have the water appearance you want—and a healthy, thriving tank to enjoy.