Algae: Red

Red algae (Rhodophyta) can be a beautiful addition to a reef aquarium, with some species being a favorite treat for fish.  On the flip side, other red algae can be quite noxious to other fish…or even invasive to coral.  With several thousand of species, red marine algae can be very difficult to identify or to characterize its place in a reef aquarium.  These are a few red algae I’ve encountered throughout the years.Red Bubble Algae (Botryocladia sp.):  Reef Safe with Caution

Most red bubble algae species do not grow to plague proportions like green bubble algae (Valonia), but it should only be kept with caution as some species do take over.  Popping the bubble can release spores, so it is best to remove the bubble algae from the base…taking a bit of rock with it.  Some people claim success with emerald crabs, but keep in mind they are spreading the spores – not killing it permanently.
Red bubble algae in the center of the photo
Red Coralline Algae:  Reef Safe
Found in just about every color and form, the encrusting coralline algae is typically desirable, especially among new aquarists.  It quickly covers dull-colored rocks, glass, and even plastic powerheads.  The desire for this decorative algae has lead to the creation of products like “Purple Up” marketed toward “fueling coralline algae growth.”  Although most aquariums will have plenty of coralline within time, it can easily spiral into a maintenance nightmare.  Once established in the aquarium it can quickly deplete the aquarium levels of calcium, magnesium, and alkalinity.  It also requires regular removal from glass/acrylic and equipment for proper functionality.  I guess my point is, “be careful for what you may wish.”
Decorative coralline algae covering dull-green rocks
Unidentified Red Fuzzy Algae:  Reef Safe
This photo was the only photo I was able to snap before my aquarium inhabitants gobbled this bit of algae up.  I would consider it reef safe as I see no way for this type to get out of hand – it was apparently a delicacy in my aquarium!
This unidentified fuzzy red algae was a treat for my fish!
Unidentified Leafy Red Algae:  Not Reef Safe
This is what I’d consider a nuisance red algae based on how it had taken over a coral.  The root structure was well-buried in the rock, so it was difficult to remove.  I ended up cutting out the coral and then throwing the rock away (well, I actually bleached the rock to reuse…I never throw rocks away.)
This red leafy algae sent runners across the rock and anchored itself into the rock
Unidentified Red Sticky Branching Algae:  Not Reef Safe
I don’t know what this one is either, but I thought it had a really neat structure.  Each little spike actually makes a mini suction cup that attaches to anything.  But, because of that, it’s nearly impossible to remove from anything (glass, rocks, etc.)  It also grows at an insane rate and will outcompete surrounding organisms.
This unique and interesting algae should be kept in a separate refugium
Red Gracilaria:  Reef Safe
This algae is a favorite food of many fish, and it is also used extensively by humans for food.  I highly recommend growing this in a refugium for the occasional fish treat.  Color will vary depending on lighting and varies from green to yellow to shades of red.
Delicious algae – for humans and fish!
Red Gracilaria Hayi:  Reef Safe
This species of Gracilaria is a bit more wide and “flame-looking”.  It’s slightly calcified, so it’s not quite the number one food of reef herbivores.  However, I’ve seen plenty of tangs go after it when they’re hungry.
This “flame-looking” algae adds an attractive touch to any refugium
Red Wire Algae (Gelidiopsis sp?):  Not Reef Safe
Red wire algae is a nightmare to remove – usually requiring manual removal with tweezers.  It was growing on top of the zoanthids in the photo, and the zoanthids would not open until the algae was removed.
Avoid this nasty red algae!


  1. Thomas Ross

    Really like the site especially the DIY and the rescues! I was blown away at the red Coralline algae pics on here! Is that in your tank and where can I get some?? I would LOVE to collect as many species of Coralline as possible, I seriously love it :). Thanks so much for all the info and putting up this site. 🙂

    1. admin

      Thank you for all the compliments! Yes, that red coralline algae was in one of my tanks nearly 10 years ago. I rarely seen that bright red color – usually I see green, purple, or pink coralline. Just keep an eye out at your LFS for various colors. However, if you plan to collect coralline colors, I recommend you have some way to maintain calcium/alkalinity/magnesium. Coralline algae is very demanding, and a calcium reactor or dosing pump is nearly essential. Good luck!

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