Aquarium Algae Control: The UK Aquarist's Complete Guide

Quick answer

Algae appears when these four things go wrong simultaneously:

1. Too much light (more than 8 hrs/day or direct sunlight)
2. Too many nutrients (overfeeding, no water changes, accumulated waste)
3. Not enough plants (no competition for those nutrients)
4. No clean-up crew (no fish/inverts eating algae as it grows)

Fix all four and algae problems vanish. Pick just one fix and algae returns.

Identifying the type of algae

Different algae have different causes and treatments:

Brown algae (diatoms)

Looks like: Brown dust coating glass, decor, and substrate. Wipes off easily. Cause: Silicates in new tank water/substrate. Normal in tanks 2-8 weeks old. Treatment: Wait 4-6 weeks; add otocinclus (group of 4-6) — they devour diatoms.

Green spot algae

Looks like: Small dark green dots on glass and slow-growing plant leaves (anubias, Java fern). Hard to wipe off. Cause: Low phosphate or excess light on slow-growing surfaces. Treatment: Nerite snails (their teeth scrape it off) + ensure phosphate isn't too low.

Green dust algae

Looks like: Soft green coating on glass. Easy to wipe but returns within days. Cause: Excess light + immature tank. Treatment: Reduce light hours; let mature; wipe weekly.

Green hair / thread algae

Looks like: Long green strands like hair, attached to plants and decor. Cause: Excess nutrients (overfeeding, too few plants) + light. Treatment: Amano shrimp eat it; manual removal weekly; reduce nutrients.

Black beard algae (BBA)

Looks like: Dark grey/black tufts on plant edges, decor, filter outlets. Hard. Cause: Inconsistent CO2 or fluctuating parameters in planted tanks. Treatment: SAE (Siamese algae eater) actually eats BBA. Spot-treat with liquid carbon (Excel/Easy-Carbo) — squirt directly onto BBA with syringe.

Blue-green algae (cyanobacteria)

Looks like: Slimy dark green/blue sheets covering substrate or decor. Smells bad. Cause: Stagnant water + excess organic waste. Treatment: Increase flow + 3-day blackout (cover tank completely) + 50% water change. Erythromycin antibiotic kills it but use as last resort.

Green water (algae bloom)

Looks like: Water turns pea-green, can't see through tank. Cause: Massive nutrient + light excess (often after over-fertilising plants). Treatment: UV sterilizer (most reliable) + 3-day blackout + reduced feeding. Daphnia eat green water — add daphnia to water if you have any.

Best algae eaters for UK tropical tanks

Browse our algae eaters category — all UK-stocked.

Step-by-step algae elimination

Week 1: Diagnose + fix root causes

1. Identify the type of algae (see chart above)
2. Reduce light to 6-8 hours per day with a timer plug (£10 from any shop)
3. Move tank away from windows if direct sunlight hits
4. Skip a feeding day to reduce nutrient input
5. Test water — high nitrate (>40 ppm) means overfeeding or no water changes

Week 2: Add clean-up crew

Based on tank size, add:

• 30-60 L: 5 amano shrimp + 2 nerite snails
• 60-100 L: 5 amano + 3 nerite + 4 otocinclus
• 100-200 L: Above + 1 bristlenose pleco
• 200 L+: Above + 1 SAE if BBA present

Week 3: Manual cleaning

• Scrape glass with magnetic algae scraper (£8)
• Trim affected plant leaves
• Vacuum substrate during weekly water change
• Clean filter media GENTLY in old tank water (don't kill bacteria)

Week 4: Add live plants

Plants compete with algae for the same nutrients. Add:

• Fast growers that absorb nutrients quickly: Hornwort, Limnophila, Vallisneria
• Floating plants that block excess light from below: Frogbit, Salvinia, Water lettuce
• Slow growers for steady aesthetic: Anubias, Java fern, Cryptocoryne

Week 5: Monitor + adjust

• Algae growth should have slowed dramatically
• If still spreading, light hours too high or feeding still excessive
• Take photos weekly to track progress

Common algae control mistakes

Mistake 1: "I'll just use algaecide chemical"

Why it fails: Kills algae fast → mass dieoff → ammonia spike → stressed fish → algae returns when chemical wears off.

Fix: Address root causes biologically.

Mistake 2: Adding plecos as "algae cleaners"

Why it fails: Common pleco grows to 30 cm and is messy. Bristlenose is what you want (12 cm). And once tank is clean, the pleco needs supplementary food (algae wafers).

Fix: Bristlenose pleco only (not common pleco). Plus shrimp + snails.

Mistake 3: Removing all algae overnight

Why it fails: Total algae removal triggers tank to regrow algae aggressively as nutrients have nothing to absorb them. Boom-bust cycle.

Fix: Gradual reduction over 4-6 weeks. Healthy tank has SOME algae always.

Mistake 4: Lighting tank 12+ hours a day

Why it fails: Algae grows exponentially with light. Plants benefit much less from extra hours beyond 8.

Fix: Timer plug, 6-8 hours daily.

Mistake 5: Only adding ONE algae eater

Why it fails: Each species eats DIFFERENT algae. One nerite won't eat hair algae; one shrimp won't eat green spot.

Fix: Combo: amano + nerite + otocinclus covers most algae types.

Prevention routine

Once tank is clean:

Following this routine, algae stays minimal indefinitely.

Summary

Algae control = light + nutrients + plants + clean-up crew. Address all four together. Use amano shrimp + nerite snails + otocinclus as the clean-up trio for most community tanks. Don't use chemical algaecides — they don't fix the cause.

Related guides

• Best Fish for a 60 Litre Tank
• Tropical Fish Tank Temperature
• Tropical Fish Water pH
• Browse algae eaters
• Browse cherry shrimp + amano shrimp