Aquarium Algae Control: The UK Aquarist's Complete Guide
Quick answer
Algae appears when these four things go wrong simultaneously:
- Too much light (more than 8 hrs/day or direct sunlight)
- Too many nutrients (overfeeding, no water changes, accumulated waste)
- Not enough plants (no competition for those nutrients)
- 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.
Light duration. Most beginners run their aquarium light 12-14 hours a day "so I can see the fish." Reduce to 6-8 hours with a £10 timer plug, and algae growth often halves within 2 weeks — with no other changes.
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
| Algae eater | Eats | Tank size | Notes |
|---|---|---|---|
| Amano shrimp (Caridina multidentata) | Hair algae, soft green algae, leftovers | 30 L+ | The most effective algae eater. 5 per 60 L. Adults safe with most fish. |
| Cherry shrimp (Neocaridina davidi) | Soft algae, biofilm | 20 L+ | Not as effective as amano but breeds in tank — colony grows |
| Nerite snail | Green spot algae, biofilm | Any size | Best snail. Doesn't breed in fresh water. Lays cosmetic eggs. |
| Mystery snail | Soft algae | 60 L+ | Larger; produce more waste than nerites |
| Otocinclus | Brown diatoms, soft green algae | 60 L+ | Tiny peaceful catfish. Group of 4+. Sensitive — only mature tanks. |
| Bristlenose pleco | Brown algae, soft greens | 80 L+ | Adult 12-15 cm. One per 100 L tank. Very effective. |
| Siamese algae eater (SAE) | Black beard algae (rare!) | 100 L+ | Only fish that eats BBA reliably. Gets to 12 cm. |
| Hillstream loach | Soft greens on rocks | 80 L+, cooler tank | River species, needs flow + 20-22 °C |
| Amano shrimp + nerite combo | Comprehensive | 60 L+ | Most flexible combo for community tanks |
Browse our algae eaters category — all UK-stocked.
Step-by-step algae elimination
Week 1: Diagnose + fix root causes
- Identify the type of algae (see chart above)
- Reduce light to 6-8 hours per day with a timer plug (£10 from any shop)
- Move tank away from windows if direct sunlight hits
- Skip a feeding day to reduce nutrient input
- 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:
| Frequency | Task |
|---|---|
| Daily | Lights on/off (timer) |
| Daily | Light feeding (small amount) |
| Weekly | 25% water change |
| Weekly | Glass scrape (front pane only — back can stay clean from snails/shrimp) |
| Weekly | One feeding-skip day |
| Monthly | Trim dying plant leaves |
| Monthly | Clean filter media in tank water (don't kill bacteria) |
| Monthly | Test water (ammonia, nitrite, nitrate) |
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.
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