Algae Troubleshooter
What kind of algae do I have, and how do I fix it?
Different algae types have different causes and fixes. Answer a few questions about what you're seeing and we'll help narrow it down, or browse the table below.
| Result | Best for |
|---|---|
| Green Water | Cloudy green water from free-floating single-celled algae |
| Brown/Diatom Algae | A brownish dusty coating, most common in newer tanks |
| Green Spot/Hair Algae | Hard green dots or stringy green growth |
| Black Beard Algae | Dark, bristly tufts, often on plant edges or hardscape |
How this quiz works
The Algae Troubleshooter asks two questions: what the algae looks like and how old your tank is. It scores the answers and points you to green water, brown or diatom algae, green spot or hair algae, or black beard algae.
Why these questions
Algae types have different causes. Green water usually points to too much light, brown dust is common in new tanks while the tank matures, green spots and hair point to an imbalance of light and nutrients, and black beard algae is linked to unstable CO2 or flow. Appearance and the age of the tank narrow these down quickly.
What the quiz cannot see
It cannot see your light, your nutrients, your CO2 or your water. Several algae types can look alike, and more than one can be present at once. Test your water, check how long the lights are on and how strong they are, and make one change at a time. Use the fertilizer and CO2 calculators if you run a planted tank.
Before you decide
Remove what you can by hand, keep up regular water changes and reduce the cause before you add treatments, since treatments can harm shrimp, snails and some plants. Do not black out a tank for days, and be patient: algae usually takes weeks, not days, to fix. Ask for help from a local fishkeeper or a planted-tank group if the problem persists.