Dealing with Problem Algae in Your Reef Tank

Algae Happens. Don't Panic.

Every reef tank gets algae. The trick isn't eliminating it entirely (impossible) — it's understanding what's there and knowing when to worry.

Brown Diatoms — The New Tank Tax

That dusty brown film on sand, glass, and rocks in the first few months? Diatoms. Completely normal. They feed on silicates present in new rock, new sand, and especially tap water.

What to do: Basically nothing. They go away on their own. A few turbo or cerith snails will graze them down. If they persist past 6 months, the RO membrane might need replacing.

Green Hair Algae (GHA) — The Common Nuisance

Stringy, bright green, often starting in high-flow spots and spreading fast.

Why it happens: Too much phosphate and/or nitrate, combined with light — usually from overfeeding or insufficient nutrient export.

What works:

Test phosphate (aim for 0.03-0.10 ppm) and nitrate (5-20 ppm)
Reduce feeding — even slightly less makes a difference
Improve skimming and add a refugium with chaetomorpha
Manual removal weekly
Grazers: sea urchins, sea hares, emerald crabs, tangs (in appropriately sized tanks)

Cyanobacteria — Not Actually Algae

That slimy red/maroon stuff that smells off and forms sheets? Cyano — technically a bacteria, not a true algae.

Why it happens: Low flow dead spots, poor oxygenation, and nutrient imbalances.

What works:

Siphon it out regularly
Increase flow in affected areas
Improve surface agitation for better gas exchange
Run chaeto in a refugium

A note on Chemi-Clean: This is specifically designed to treat cyanobacteria — not a general algae cure. It targets bacteria, so it can also affect beneficial bacterial populations. Follow instructions exactly, run extra aeration, and do a water change afterwards.

Bubble Algae

Small dark green spheres on rocks. Remove without popping them — the bubbles contain spores. Twist gently and remove from the tank. Emerald crabs sometimes eat them, but inconsistently.

The Long-Term Fix

Most algae problems come down to nutrient export:

Good protein skimmer — probably the single most important piece of equipment for algae control
Chaeto refugium — nature's nutrient sponge
Appropriate feeding — less is almost always more
Regular water changes — dilution is underrated

Don't chase zero nutrients though. Corals need some nitrate and phosphate. A sterile tank is just as problematic as a dirty one.