Algae
3 topics in this section
The Definitive Guide to Algae: Identification, Causes, Risks, and Removal of Every Type of Algae That Can Appear in Freshwater and Saltwater Aquariums.
What is an alga?
Algae are photosynthetic organisms that do not belong to the plant kingdom. There are several distinct taxonomic groups that we commonly refer to as "algae":
| Group | Aquarium Examples | Features |
|---|---|---|
| Chlorophytes (green algae) | GHA, GSA, GDA, Cladophora | Chlorophyll a+b; green pigmentation |
| Bacillophytes (diatoms) | Brown diatoms | Siliceous wall; brown/gold color |
| Rhodophytes (red algae) | BBA, Staghorn | Phycoerythrin; resistant |
| Cyanobacteria | Oscillatory | Photosynthetic prokaryotes; odor |
| Dinoflagellates | Marine dinosaurs | Mixotrophs; potential toxins |
| Feofitas (brown algae) | Caulerpa (green), Bryopsis | Fucoxanthin; found only in marine organisms |
Important: Cyanobacteria are not algae in the strict sense; they are photosynthetic bacteria. However, they behave and are treated similarly, which is why they are included in this guide.
Why Does Algae Grow?
Algae are opportunistic: they colonize any environment where they find the resources they need. Algae spores and cells are always present in an aquarium; the problem arises when conditions favor their proliferation.
Factors that promote algae growth
| Factor | Problem Situation | Effect |
|---|---|---|
| Excessive light | More than 8–10 hours per day or too high an intensity | Energy for Accelerated Growth |
| Inadequate lighting | Incorrect spectrum or PAR for the plants | Plants don't compete, but algae do |
| Excess Nitrates (NO₃) | > 20 ppm in planted tanks, > 5 ppm in marine tanks | Algae Fertilizer |
| Excess Phosphates (PO₄) | > 0.1 ppm in freshwater, > 0.05 ppm in saltwater | Primary seaweed fertilizer |
| CO₂ Deficit | Grown without CO₂ or with inconsistent injection | Plants aren't growing; algae are taking over |
| Ammonium (NH₄⁺/NH₃) | Any detectable level | Algae consume it directly |
| Nutrient Imbalance | Imbalanced N, P, K, and Fe | Algae make use of the excess |
| New Aquarium | Unfinished cycle, no bacteria | No competition, no stability |
| Supercharging | Uneaten food | Increases NH₃, NO₃, and PO₄ |
| Overpopulation | Plenty of fish to fill the tank | Excessive organic load |
| Insufficient filtration | It does not process the biological load | Nutrient Accumulation |
| Insufficient water changes | Nitrates and phosphates accumulate | High chronic level |
The Algae Triangle
Plants and algae compete for the same three resources. If there is an imbalance at any vertex, the algae win:
- High light + low nutrients + low CO₂ → plants cannot utilize the light → algae
- Low light + lots of nutrients → plants don't grow → algae
- Inconsistent CO₂ → pH fluctuates → stressed plants → algae
- Balanced nutrients + stable CO₂ + adequate light → vigorous plants → no problematic algae
Comprehensive Algae Control Strategy
For freshwater (planted aquarium)
- Stable CO₂: Set the timer to start 1–2 hours before the lights come on. High-quality diffuser. Target level: 20–30 ppm. Do not turn on or off abruptly.
- Light-to-plant ratio: Increase plant density. Use fast-growing plants (Hornwort, Egeria, Rotala) as competitors.
- Controlled photoperiod: 6–8 hours. Use a light break (turn off for 2 hours at midday) to reduce the effective duration without losing intensity.
- Balanced fertilization: EI (Estimative Index) or PPS-Pro ensure that there are neither deficiencies nor excesses of any nutrients.
- Water changes: 30–50% weekly to reset nutrient buildup.
- Filter cleaning: Monthly to prevent the buildup of organic matter.
- Biological combo: Otocinclus + Nerite snails + Amano shrimp—it's the holy trinity.
For seawater (reef)
- RO/DI Water: Required. 0 TDS at the inlet.
- Optimized skimmer: Remove "wet" (dark brown) foam regularly.
- Hideout with Chaeto: Chaetomorpha in a hideout lit for 18–24 hours (cycle opposite to the display tank) to export nutrients.
- Nutrient ranges: NO₃ 1–10 ppm, PO₄ 0.02–0.10 ppm. Neither too high nor too low.
- Water circulation throughout the entire tank: No dead zones. Powerheads at the bottom of the sump as well.
- Cleanup crew (CUC): A mix of herbivores: tangs, snails, hermit crabs, and sea urchins.
- ICP: Periodic test to detect trace element imbalances.
- Quarantine: All new material is quarantined for 4–6 weeks.
Universal Golden Rule
Identify the cause before treating the symptom. Algae are indicators, not the problem itself. If you remove the algae without addressing the root cause, it will come back.
Section 17 — Algae in the Aquarium | Tankily Wiki
Quick Reference Summary Table
| Color | Texture | Water | Probable Alga |
|---|---|---|---|
| Dusty brown | It comes off easily | Sweet/Marina | Diatoms |
| Fine, dusty green | It comes in sheets | Sweet | GDA (green dust) |
| Dark green, circular spots | Hard, adhering | Sweet | GSA (green spot) |
| Light green, soft highlights | It rolls up easily | Sweet/Marina | GHA (hair algae) |
| Black/dark gray, streaks | Very thick, beard | Sweet | BBA (Black Beard) |
| Light gray, Y-shaped | Rigid, fragile | Sweet | Staghorn |
| Blue-green/red, mantle | Gelatinous, strong odor | Sweet/Marina | Cyanobacteria |
| Opaque green water | Not visible (suspended) | Sweet | Green Water |
| Emerald green, feathery | Soft, chewy | Marina | Bryopsis |
| Golden brown with bubbles | Mucilaginous, with gas | Marina | Dinoflagellates |
| Bright green, spheres | Hard, smooth bubble | Marina | Wallonia |
| Pink/purple, hard crust | Incrustant, limestone | Marina | CCA (preferred) |