Algae Control: Root Cause Playbook

Why algae wins: light and nutrients out of balance

Algae is not an infection; it is the evolutionary default state of water. It has existed for billions of years and requires almost zero energy to reproduce. Plants, by comparison, are complex and demanding.

• The Competition: Plants and algae compete for the same resources (Light, Nitrogen, Phosphorus).
• Allelopathy: Healthy, fast-growing plants release chemical inhibitors (enzymes) that suppress algae spores.
• The Trigger: Algae blooms only occur when plants stop growing. If a "limiting factor" (like low CO2) stalls plant metabolism, they stop producing enzymes. The algae detects this weakness and blooms immediately.

Identify your algae and fix its cause

You cannot treat "algae" generically. You must identify the specific strain to understand the specific imbalance.

Diatoms (Brown Algae)

A soft, brown, dusty coating on glass, substrate, and plant leaves.

• The Cause: High Silicates (SiO₂) and immature biological filtration. Extremely common in new tanks (<2 months old).
• The Fix:

1. Patience: It usually disappears on its own once the tank matures.
2. Biological: Add Otocinclus Catfish (6+ school). They consume diatoms voraciously.

Green Spot Algae (GSA)

Hard, dark green circles on glass and slow-growing leaves (Anubias). Hard to scrape off.

• The Cause: Excess Light intensity or Low Phosphate (PO₄) levels.
• The Fix:

1. Lighting Lab Check: If your Surface PAR is >100 ("Algae Risk"), dim your lights by 15%.
2. Chemistry: Increase Phosphate dosing.
3. Biological: Nerite Snails are the only clean-up crew strong enough to rasp GSA off surfaces.

Black Beard Algae (BBA)

The nemesis of aquarists. Dark, fuzzy, grey/black tufts on driftwood, filter outlets, and leaf edges.

• The Cause: Fluctuating CO2 levels (unstable injection) or dirty filters (high organic waste). It loves high-flow areas.
• The Fix:

1. CO2 Stability: Ensure your Drop Checker is lime green before the lights turn on.
2. Filter Hygiene: Check Filter Media Health in the app. If flow is reduced, organic waste is rotting in the filter, feeding the BBA.
3. Chemical Spot Treatment: Turn off the filter. Use a syringe to squirt "Liquid Carbon" (Glutaraldehyde) or Hydrogen Peroxide (H₂O₂) directly onto the tufts. They will turn red/white and die within 24 hours.

Cyanobacteria (Blue-Green Slime)

Not actually algae, but a photosynthetic bacteria. It forms a slimy, blue-green blanket that smells like swamp mud.

• The Cause: Extremely low Nitrates (0 ppm) or Dead Spots (zero flow areas).
• The Fix:

1. Filtration Lab Check: Analyze your flow. If you have dead spots, add a circulation pump to keep water moving.
2. Antibiotics: Erythromycin (Maracyn) kills it effectively, but can harm your bio-filter. Use as a last resort.
3. Blackout: It cannot survive 3 days without light.

Filamentous (Hair/Thread) Algae

Long green strands that tangle in moss and stem plants.

• The Cause: Low CO2 combined with High Light, or an Ammonia spike in a new tank.
• The Fix:

1. Manual Removal: Use a toothbrush to twirl it out like spaghetti.
2. Biological: Amano Shrimp are the kings of hair algae. Stock 1 per 2 gallons.
3. Lighting: Reduce photoperiod to 6 hours.

Clean-up crews that actually help

Don't fight alone. Hire a janitorial staff to manage the micro-growth before it becomes visible.

• Amano Shrimp (*Caridina multidentata*): The heavy lifters. They eat hair algae, uneaten food, and decaying plant matter.
• Stocking:* 1 per 2–3 gallons.
• Nerite Snails: The tank scrapers. They eat Green Spot Algae and Diatoms. They do not reproduce in freshwater (no snail plagues).
• Stocking:* 1 per 5 gallons.
• Otocinclus Catfish: Delicate leaf cleaners. They gently polish surfaces without damaging plants.
• Stocking:* 6+ (Schooling). Only add to mature tanks (>3 months old) with established biofilm.
• Siamese Algae Eaters (SAE): The only fish that eats BBA.
• Warning: They grow large (6 inches) and can be aggressive. Only for tanks >40 gallons.

The blackout method (emergency reset)

If algae has taken over >50% of the tank biomass, use the nuclear option.

1. The Trigger: Turn off CO2 and Lights.
2. The Cover: Wrap the tank in heavy blankets or black trash bags. Zero light must enter for 3 full days.
3. The Logic: Plants store energy (starch/sugar) and can survive 3 days of darkness. Algae has no storage capacity; it starves and dies.
4. The Aftermath: On Day 4, uncover the tank. The algae will be grey/dead. Perform a 50% water change to remove the decaying spores and ammonia.

Preventing the next outbreak

The Lighting Lab

Algae thrives on "wasted" light energy.

• The Check: Open the Lighting Lab. Look at your PAR at Depth.
• The Risk: If your Surface PAR is 250 (Algae Risk) but you are not injecting CO2, you are providing "high acceleration" with "no fuel." Algae will utilize that excess energy.
• The Adjustment: Lower the intensity until the "Algae Risk" warning disappears or PAR drops to the "Medium" range (40–90 PAR).

The Health Lab Monitor

Algae spores are triggered by Ammonia spikes (instability).

• The Check: Monitor the Water Quality Stability bar.
• The Insight: If stability drops, it means your bioload is overwhelming your filter. This trace ammonia triggers algae spores to bloom.
• The Action: If the Lab warns of instability, perform a water change immediately and stop feeding for 2 days to let the bacterial colony catch up.