Driftwood and rocks for aquariums: which ones are safe for your fish?
Golden rule: a safe piece of driftwood or rock either doesn’t change your water chemistry… or changes it the way you want. Mangrove, mopani and spider wood are harmless; on the mineral side, beware of limestone, which hardens the water. A simple vinegar test and proper preparation prevent 90 % of accidents.
Which types of wood are safe choices?
- Spider wood (redmoor): 15 to 40 €, very decorative, floats for a long time before becoming waterlogged.
- Mangrove and mopani: 10 to 30 €, dense, sink quickly, release a lot of tannins.
- Driftwood from the aquarium trade: always safe if sold for aquarium use.
- Off limits: resinous woods (pine, fir), varnished or treated wood, and unidentified, undried branches picked up outdoors.
The tannins released tint the water amber and acidify it slightly: harmless, even beneficial for bettas, shrimp and Amazonian fish. Soaking for one to two weeks, with regular water changes, reduces the colouring.
How do you know if a rock is limestone?
Drip a little white vinegar onto it: if it fizzes, the rock is calcareous and will push up GH, KH and pH. That rules it out for an Amazon tank, but it’s exactly what African cichlid keepers want. Safe, neutral rocks: slate, quartz, granite, dragon stone, lava rock (watch the sharp edges). Calcareous rocks: seiryu (slightly), white limestone, tufa, marble. Check the real effect with your water tests in the weeks after adding them.
How should driftwood and rocks be prepared?
Scrub under hot water without soap, then boil small pieces of wood for 30 to 60 minutes: this speeds up sinking and kills spores and parasites. Large pieces get soaked in a container. Rocks are scrubbed and doused with boiling water. If collecting in the wild, only take hard stones far from farmland, and never metal-bearing rocks (rust marks or metallic glints).
How much rock weight can a tank take?
Place large rocks directly on the bottom pane (on a thin polystyrene sheet or a plastic grid), before the substrate goes in — never balanced on gravel that a digging fish can undermine. A stone-heavy aquascape quickly adds 10 to 20 kg: check the capacity of your aquarium stand. More safe-decor ideas in the decor and plants category.
Frequently asked questions
My driftwood is growing a white film — is that serious?
No, it’s a harmless biofilm of bacteria and fungi, common in the first weeks. Shrimp and otocinclus feast on it; otherwise, siphon it off.
Can I use seashells or coral?
Only in hard, alkaline water (African cichlids, some livebearers): they are concentrated limestone and drive hardness up.
Can driftwood rot in the tank?
Genuine aquarium wood breaks down over years without any danger. If it turns spongy and foul-smelling, it was the wrong kind of wood: remove it.
This guide is part of Planète Pets’s Fishkeeping universe. Our advice is general in nature: for any health concern, your veterinarian remains the only reference.