Chaetomorpha vs Caulerpa


There has been quite a bit of debate on which algae, caluerpa or chaetomorpha, is best for the home aquarium. Both perform the same functions and both have the same requirements, but there are stark differences between the two plants that make the choice difficult sometimes.


Caulerpa comes in a variety of flavors. There is grape caulerpa, razor caulerpa, feather caulerpa, and many more. For the most part, they are extremely fast growers and make an excellent home for amphipods, stomatella snails, bristleworms, and all of the other fantastic refugium life. It also excellent for nutrient control. Some caulerpa species are better than others. Some grow more quickly or more slowly, some lay out “runners” with which to attach to the substrate, and some have long leaves that make them excellent for a seagrass tank. But caulerpa has several severe drawbacks. It can go sexual, overgrow equipment and corals, and can produce chemicals that reduce coral growth and stain the aquarium water.

Caulerpa has a nasty side to it…and that is its ability to “go sexual”. When caulerpa goes sexual, it turns white, dissolves, and releases spores and all of the nutrients it had previously absored back into the system. These excess nutrients and spores can cause a massive tank crash. The tank will become very cloudy and the only way to battle it is a massive water change. But there are methods aquarists use to keep the caulerpa from going sexual. Some swear that keeping the lights on the caulerpa (in the refugium) 24 hours a day, 7 days a week will prevent the caulerpa from going sexual. However, in my experience, caulerpa has done better when given a long period where it is illuminated followed by at least 8 hours of darkness. This just so happens to be one of those “what works best for you” situations. If your caulerpa goes sexual with a 24/7 photoperiod, then change it around to find what works.

Grape Caulerpa

Grape Caulerpa

Another downside to caulerpa is it’s destructive behavior. Caulerpa grows extraordinarily fast, sometimes fast enough to destroy equipment. For example, I had a small pump in my refugium to provide a little extra flow. Everything was doing well, and then I noticed a burning smell. I couldn’t find it at first, but following my nose I eventually found it. The caulerpa had grown into the pump and had stopped the impeller from spinning. The motor kept moving, but the pump eventually burned up. Although a blessing for the most part, caulerpa’s quick growth rate has led to other problems as well. Worldwide, caulerpa has grown so fast that it has destroyed natural reefs. There are even organizations that have been established to help erradicate and prevent caulerpa from absolutely taking over. In California, the group SCCAT, or the Southern California Caulerpa Action Team has been established to help educate people about caulerpa and help to rid local waters of it. Caulerpa has even been banned in California for fear of it getting into the ocean and spreading. Also be weary of any caulerpa getting into your display tank. It will overgrow corals and will be extremely difficult to remove.

Finally, caulerpa has a noxious, and sometimes toxic, aspect to consider. It has long been acepted too that grape caulerpa will release chemicals into the water that will inhibit the growth of your corals. This type of “chemical warfare” is a way of insuring its survival. This sort of behavior is similar to what a lot of corals do. Since real estate is usually non-existent on a natural reef, corals and other organisms have developed methods of harming or killing their neighbors in order to either gain space, or fight what they’ve already got. A lot of reefkeepers swear that caulerpa inhibits the growth of their corals…especially SPS, and most fish will not eat it. I have used grape caulerpa for years and have not experienced any of the drawbacks that a lot of aquarists have expressed.

Here is an amazing story of caulerpa going sexual. The author took several pictures leading up to the event.
A Warning Sign of Impending Caulerpa Sporulation


Chaetomorpha is probably the best overall algae for the refugium. It doesn’t attach to the substrate like caulerpa, but sits in a dense ball that looks like a big brillo pad or bundle of spaghetti. There are only a handful of species available to the everyday hobbyist, but the differences between each of the commonly used species are slight and each one serves the same purpose.

Chaetomorpha Macroalgae

Chaetomorpha Macroalgae

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Unlike caulerpa, chaetomorpha (abbreviate chaeto) does not grow onto the rocks or sand, but stays in a floating mass. It will not grow onto powerheads, and if it were to get into your display, it could easily be removed by a net or by hand. You will not have the same battle with chaeto like you would if caulerpa got into your display. Chaeto also has the huge advantage in that it does not go sexual. It may whither and die in some setups, but overall it is hardy and will not release nutrients back into the system causing a tank crash.

Being dense, chaeto makes for an excellent home for amphipods and other small refugium organisms. The density also has a downside. If the ball of chaeto is too thick, the light cannot penetrate to the underside of the mass. The underside may die or lose some pigmentation, but there is a solution. If you place a powerhead into the refugium and point it at the floating chaeto, it will cause it to spin or tumble. As it rotates in the water, the light will hit most surfaces of the plant and will prevent dead spots from forming.

With all that being said, do not count out caulerpa (unless you are in California). I have used it for years with absolutely no problems. I have never had caulerpa go sexual, but I have lost a cheap pump to it. One further thing I would like to mention is sometimes a tank, for whatever reason, cannot sustain one algae or the other. For example, I had a very difficult time maintaining chaeto in my 90 gallon mixed reef when it was setup. In my 180 I had a much easier time keeping it alive, although it grew very slowly. Caulerpa on the other hand has been rock solid for me. It grows so unbelievably fast and I’ve never had problems getting it to grow.

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