Saltwater Algae

Saltwater Algae, Cyano & Dino Guide

Not everything growing in a reef tank is the same. Hair algae, cyanobacteria and dinoflagellates can look similar but often require very different solutions.

First — identify what you're dealing with.

Don't immediately start adding chemicals or stripping nutrients from the aquarium. Some problems are caused by excess nutrients, while others can appear when nutrients have been driven too low.

Green Hair / Turf Green strands or fuzzy growth
Cyanobacteria Red, purple or dark slimy mats
Dinoflagellates Brown strings, often with bubbles
Bryopsis Feathery or fern-like green algae
Diatoms Brown dusty coating
Bubble Algae Green round bubbles

Green Hair & Turf Algae

Green strands, fuzz or thick green growth on rock

Green hair algae is one of the most common saltwater algae problems. It usually grows from rockwork and can range from short green fuzz to long flowing strands.

Natural Control
  • Pull or scrub out as much as possible.
  • Siphon loosened algae during a water change.
  • Reduce overfeeding and accumulated waste.
  • Turbo and Trochus snails are excellent grazers.
  • Urchins can be excellent algae grazers in appropriate tanks.
If It Keeps Returning
  • Check nitrate and phosphate.
  • Clean mechanical filtration regularly.
  • Reduce an unnecessarily long lighting period.
  • Correct excessive nutrients gradually.
Wet Pets Recommendations: Mexican Turbo Snail · Red Stripe Trochus Snail · Short Spine Sea Urchin · Algae Eating Sea Hare

Cyanobacteria — Red Slime

Red, burgundy, purple or dark slimy sheets

Cyanobacteria is bacteria rather than true algae. It often forms slimy mats across the sand or rock and can usually be siphoned away fairly easily.

Natural Control
  • Siphon out as much as possible.
  • Remove accumulated detritus.
  • Improve circulation in dead spots.
  • Make sure nitrate and phosphate are not bottomed out.
  • Maintain good filtration and skimming.
Treatment
  • Clean the tank and remove as much slime as possible first.
  • Fritz Slime Out can be used for persistent cyanobacteria.
  • Follow the product directions exactly.
  • Maintain strong aeration during treatment.
Wet Pets Recommendation: Fritz Slime Out

Dinoflagellates — Dinos

Brown or golden stringy growth, often with trapped air bubbles

Dinoflagellates often appear as brown or golden strings or slime across the sand and rocks. Bubbles frequently become trapped in the growth, especially as the lights remain on.

Important: Don't assume dinos mean your nutrients are too high.
Dinoflagellates commonly become problematic in very clean reef aquariums where nitrate and/or phosphate have been driven extremely low or to zero.
What to Do
  • Test nitrate and phosphate.
  • Do not keep stripping nutrients if they are already near zero.
  • Siphon visible dinos from the aquarium.
  • Keep the aquarium biologically stable.
  • Encourage healthy competing microorganisms.
If Nutrients Are Zero
  • Bring nitrate and phosphate back into measurable ranges.
  • Make corrections gradually.
  • Do not blindly add phosphate remover.
  • UV can help with some types of dinoflagellates.
For Low Nutrients: Brightwell NeoNitro · Brightwell NeoPhos · Wet Pets Dosing Calculator

Bryopsis

Green algae with a distinctive feather or fern-like appearance

Bryopsis can initially look like ordinary hair algae, but the strands develop a distinctive feathery or fern-like structure. It can be extremely stubborn once established.

Natural Control
  • Manually remove as much as possible.
  • Remove affected removable rocks when practical.
  • Reduce accumulated organic waste.
  • Some grazers may pick at it, but don't rely on livestock alone.
Treatment
  • Bryopsis can be much harder to eliminate than ordinary hair algae.
  • BlueLife Flux Rx is an option for persistent Bryopsis.
  • Follow the complete product directions carefully.
Wet Pets Recommendation: BlueLife Flux Rx

Brown Diatoms

Soft dusty brown coating on sand, rock and glass

Diatoms look like a dusty brown coating and are extremely common in newer saltwater aquariums. They often appear during the normal maturation of a new reef.

Natural Control
  • Give a newer aquarium time to mature.
  • Clean the glass normally.
  • Siphon the surface of the sand when needed.
  • Trochus and Astrea snails graze surface growth.
  • Urchins can help clean established rockwork.
Usually No Chemical Is Needed
  • Use good-quality RODI water.
  • Continue normal maintenance.
  • Avoid making major changes just because diatoms appear.
  • They often decline as the aquarium matures.
Wet Pets Recommendations: Red Stripe Trochus Snail · Astrea Turbo Snail · Short Spine Sea Urchin

Bubble Algae

Smooth green bubbles growing from rockwork

Bubble algae forms round green bubbles that may occur individually or in clusters. It commonly grows in crevices where it can be difficult to reach.

Natural Control
  • Carefully remove bubbles from the rock when possible.
  • Remove affected rocks for cleaning when practical.
  • Emerald crabs may eat bubble algae.
  • Reduce excessive nutrients and trapped detritus.
Best Approach
  • Physical removal is usually the first choice.
  • Don't rely on a general algae treatment as the primary solution.
  • Keep the aquarium clean to reduce regrowth.
Don't Forget About Detritus.

Leftover food and organic waste can accumulate in the sand and rockwork, feeding nuisance algae and cyanobacteria. A clean-up crew helps, but it does not replace normal aquarium maintenance.

Baja Nassarius Snail  ·  Mexican Turbo Snail

High nutrients and zero nutrients are both problems.

If nitrate or phosphate is high, reduce it gradually through improved maintenance, water changes and nutrient control. If nitrate or phosphate is already zero, do not automatically add more nutrient-removing media.

BlueLife Phosphate Rx — for situations where phosphate actually needs to be reduced.

Brightwell NeoNitro  ·  Brightwell NeoPhos — for situations where nutrients are too low.

Which Clean-Up Crew?

Different animals are better suited for different jobs.

Hair Algae Turbo Snails
Trochus Snails
Urchins
Film / Diatoms Trochus
Astrea
Urchins
Heavy Hair Algae Sea Hare
Turbo Snails
Sand / Detritus Nassarius Snails
Conchs
Don't try to make nitrate and phosphate zero. Reef tanks need nutrients. Aggressively stripping nitrate and phosphate can destabilize the aquarium and may create conditions favorable to dinoflagellates or other unwanted organisms. The goal is controlled, measurable nutrients — not sterile water.

The Simple Wet Pets Plan

1
Identify It Hair algae, cyano, dinos and diatoms are different problems.
2
Remove It Siphon, scrub or manually remove as much as practical.
3
Check Nutrients Know your nitrate and phosphate before changing them.
4
Treat the Cause Add grazers or use a targeted treatment when appropriate.

Some algae is completely normal in a saltwater aquarium. The goal is a stable reef where nuisance growth remains under control. If you aren't sure whether you're looking at algae, cyanobacteria or dinoflagellates, take a clear photo and bring it to Wet Pets Aquatics along with your nitrate and phosphate results. Correct identification can completely change the recommended treatment.