Chaetomorpha | Best Macroalgae for the Refugium

In my opinion, the very best macroalgae for your saltwater aquarium’s refugium is chaetomorpha. Generally considered too unsightly to be placed in the main display tank, chaetomorpha is a wiry mass of coarse, stringy algae with the color of a green dishwashing scouring pad.

refugium with chaetomorpha

Refugium with chaetomorpha

Chaetomorpha grows by absorbing nitrates and phosphates from aquarium water, much like how terrestrial plants absorb nitrates and phosphates from the soil or from fertilizer to grow. And it is precisely this capacity for nutrient absorption that makes chaetomorpha one of our best allies when it comes to nitrate and phosphate reduction in our saltwater tanks.

And under the right refugium lighting, chaeto growth can be exponential!

Chaetomorpha | A Safe Haven for Copepods

Ahhh, copepods. A delectable live food for our fish and corals. Every reefkeeper just can’t get enough of these little critters.

In nature, copepods are abundant and are part of the planktonic soup that form our oceans. No wonder so many marine organisms depend on them for food and survival. In our article on Mandarin Fish Care and Feeding we talked about how critical having a sizeable copepod population was to the survival of wild-caught Mandarin Fish that have not been trained to accept prepared foods.

But in the closed environment of or saltwater aquariums, copepods are consumed quickly — very often faster than they can reproduce.

It is my opinion that, along with some live rock in the refugium, a tangled mass of chaetomorpha is one of the best ways to encourage copepods to reproduce.

The refugium compartment in my sump is always teeming with these little critters — tiny white bug-like creatures that seem to dart about constantly and nervously — a testimony to their survival instinct because they are so delicious to fish!

Many of these ‘pods find their way back to the main tank through the return pump and take up residence on the rocks. In my tank, they are often seen hanging out on the aquarium glass where my yellow-tailed blue damsel ‘Bluey’ picks them off for a quick snack once in awhile. I estimate that size-wise, a copepod is to Bluey what a piece of sushi is to me!

Chaetomorpha | Food for Herbivorous Fish

I found this out for myself when I was shaking out a clump of chaeto into the main tank to get some of the copepods directly to the fish and corals.

To my surprise, my yellow tang made a dash for the clump of chaetomorpha that I was holding and managed to pull away a single, long strand with her mouth which she proceeded to slurp up like spaghetti. My yellow tang certainly does enjoy her occasional chaeto treat. So much for reading about chaetopmorpha being unappetizing to fish!

Now I cannot guarantee that your herbivorous fish will take to eating chaetomorpha like my yellow tang, but give it a try. You just might be surprised.

Chaetomorpha and Phosphate Remover

I have learned that chaetomorpha does not do well in my tank when I use a phosphate remover. I always see a sizeable chaetomorpha die-off when I introduce phosphate remover. With the phosphate remover removed — I use Rowaphos from time to time whenever I see a brown diatom bloom coming on — the chaetomorpha recovers after a few weeks and continues to grow rapidly. Chaetomorpha needs phosphate, it seems, as much as it needs nitrates to grow. I have to be careful not to kill off the chaetomorpha entirely, due to lack of phosphates, when I use Rowaphos.

Again this is up to what I would call the ‘chemical personality’ of your tank. I know of many reefers who have good chaetomorpha growth while running phosphate remover 24/7. Go figure.

Caulerpa | The Macroalgae To Avoid At All Costs!

This is probably going to annoy some reefkeepers who embrace Caulerpa as their macroalgae of choice.

First off, let me say this — Caulerpa is fine as long as you keep your refugium lit 24 hours a day. When placed on a day and night cycle, it is only a matter of time before Caulerpa goes sexual.

The once lush green fronds of Caulerpa turn translucent and limp while releasing milky white, reproductive spores that make your refugium and your main display look like someone had dropped a vanilla ice-cream cone in your tank.

When a large amount of chaetomorpha go sexual, oxygen levels drop and fish behave skittishly and start hiding.

And when Caulerpa go sexual, they will all go sexual at the same time. Not a single green frond will remain after such an episode and the aftermath of a big water change and siphoning out the dead plant material is something I would rather not deal with.

As you can see in this picture of the fiancee’s nano seahorse tank, it didn’t take very much Caulerpa to create this

Caulerpa going sexual

Caulerpa going sexual in a seahorse tank

milky mess. And to think that the Caulerpa in this tank was naturally-ocurring — it wasn’t there when we added this piece of live rock — and simply appeared and grew out and spread by itself. Fortunately there were no casualties from this episode.

Chaetomorpha really is my favorite macroalgae. It does it’s job and best of all, it behaves!

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