The Algae Stages of a New Planted Tank (and How to Ride Them Out)
New tanks almost always go through a predictable wave of algae as they mature. Here's the rough timeline — diatoms, then filamentous, then maturity — and what to do at each stage.
New tanks get algae, and that's normal
The 2Hr Aquarist notes that in a tank under about 3 months old it is common to get an initial bout of algae as the plants adapt to their new environment. What makes a mature tank stable is the microbial population it builds up, and that biological maturity takes a few weeks beyond the point where the ammonia cycle itself is finished.
The rough timeline
- First 1-3 weeks: brown diatom dust on glass, substrate and leaves — the 2Hr Aquarist treats this as a near-certain sign the system is still immature.
- First 1-2 weeks: a sudden burst of filamentous algae (hair / thread) can appear as plants go through transition stress.
- As it matures (around 6-8 weeks): the diatoms fade on their own and you may see green spot or green dust on the glass — this is the spread of maturity, not a failure.
What to actually do
Keep the light modest and stable — Tropica suggests 6 hours a day for the first 2-3 weeks, then increasing to 8-10 hours — and do generous water changes, around 25-50% a couple of times a week for the first 3-4 weeks. Add snails and shrimp early to graze the films, but delay adding fish for about 3-4 weeks until the plants have established.
Let biology win
The 2Hr Aquarist is reassuring here: diatoms disappear once the tank matures without any other intervention, and healthy, established plants make the whole system much harder for algae to take hold in. Reaching a good level of maturity typically takes about 6-8 weeks — patience is the main tool.
Sources: The 2Hr Aquarist, Algae and tank maturity and How to get rid of brown algae (diatoms) (www.2hraquarist.com www.2hraquarist.com); Tropica Plant Guide, Starting a new aquarium (tropica.com).