Reef Discussion

Using Seaweed To Get Rid Of Nuisance Algae In Your Aquarium Or Pond
One of the neat things about nature is that it's had a long time to figure things out. Especially under water. Here, nature has figured out how to reduce all the "nutrients" to very low values, and also how to feed every aquatic animal (as well as consume half the world's CO2, and produce half the world's oxygen), by just using sunlight. Not bad. Maybe this concept can be used to help your water pets.

Well of course it can. And it is already doing so, sort of. It's just not being used enough, or even on purpose. It's sort of the difference between a bicycle and a motorcycle, or a snack and a big dinner. Or even knowing you have a dinner in the first place. It's called photosynthesis.

You have all heard about photosynthesis; it reminds you of trees and science experiments. But how can it help? Well the basics are this: Photosynthesis takes carbon out of carbon dioxide, and uses it to build living things, and it releases oxygen in the process. You've probably also heard that all living things contain carbon; well, that's where the carbon comes from, and photosynthesis is how it got there. The living things that photosynthesis builds generally are plants (on land) and algae (seaweed and phytoplankton) in the water. Then, anything (like you) that eats these plants or seaweeds will get the carbon you need to grow. Oops, there is one more neat thing that photosynthesis does when building these living things: It uses Ammonia, Nitrite, Nitrate, Phosphate, and many metals like Copper and Iron too.

Sounds like an ideal filter, right? Removes Ammonia, Nitrite, Nitrate, Phosphate, CO2 and metals, and put oxygen into the water. Also sounds like an ecosystem, like the ocean, or lakes, or rivers. Because it is! That's how the oceans, lakes and rivers are naturally filtered!

So we will be showing you how to build your own DIY versions of these neat filters (for fresh or salt) in the coming posts.
 

Trash

Member
Jan 21, 2013
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Sounds good to me. Is it like having macro algae growing in the sump? I remove clumps of the stuff every month.
 
Using Seaweed to get rid of nuisance algae in your aquarium or pond, part 2

So how does photosynthesis "pull" the carbon it needs out of the air or water? Doesn't CO2 or other nutrients just "soak" into things by themselves? For example, doesn't CO2 just soak into trees? Meaning, if you have more trees, won't more CO2 just soak into them? No, not really.

CO2 and other things do "soak" into water, but the reason that the water does not "fill up" with CO2 is because organisms in the water "pull" and "eat" the CO2. What organisms might these be? Algae, of course. Or more specifically Photo-Auto-Trophs (photoautotrophs), which means they get their food (carbon) all by themselves (auto), without needing to eat other animals, and they do this using sunlight (photo). In the open ocean and open lakes, all this is done by free-floating algae (phyto plankton), but as you the get to shallower areas of the reefs and lake shores (and in streams and shallow rivers), it is done by benthic (attached) algae on the bottom surfaces. We will be calling all attached algae "seaweed", even if it's in freshwater lakes, because saying "lakeweed" is a bit odd.

The faster that carbon is taken out of the water by the seaweed on the bottom surfaces, the faster CO2 can continue to absorb into the water at the water's surface. This is an important idea to understand; it forms a CO2 "gradient". This idea is easier to explain by thinking about an oven: Standing far away from an oven, you might barely feel the heat, but as you move closer to the oven, your temperature rises. So even though the oven is making the same heat, the amount of heat you feel depends on how close you are to it.

With seaweed on the bottom of the reef or lake, the amount of CO2/carbon the seaweed "feels" depends on (among other things) how close the seaweed is to the surface of the water where the air is, because this is where CO2 is being absorbed into the water from the air. This is one of the reasons (besides light) why all the phytoplankton lives near the surface of the water. Seaweed however is far from the water surface, and water that is next to the seaweed (say, 1 cm away) has had so much carbon removed that there might be little carbon remaining. So by making the air more near to the seaweed, it feels and has access to more CO2/carbon. This "near-ness" of air to the seaweed is what makes things work for our filtering needs.
 
What is Periphyton?

Periphyton is what turns your rocks different colors. You know... the white rocks you started with in saltwater, or the grey rocks (or brown wood) you started with in freshwater. After several months or years, the rocks become a variety of different colors and textures. Why? Because the periphyton that has grown on it is a mix of different living things, with different colors, and thicknesses. And the important part is: It is LIVING. And the thicker it is, the more living material there is.

That's right: The colored stuff that has coated your rocks is all living organisms. Sponges, microbes, algae, cyano, biofilms, and of course coralline in saltwater. After all, "peri" means "around the outside", and "phyto" means "plant". Have you ever slipped while walking on rocks in a stream? That's the periphyton that made it slippery. It can be a very thin coating on the rocks, sometimes paper thin, but it covers the entire surface, especially across the top which gets more light.

There is a lot of photosynthetic organisms in periphyton, and this means that they need light; but they need nutrients too (ammonia, nitrate, phosphate). And as you might guess, the organisms will prefer the illuminated portions of the rocks, and will grow to intercept food particles in the water, based on the water flow. Just think about how sponges orient their openings for water flow; the micro sponges in periphyton do it too, but on a tiny scale.

What about in caves and holes? Well periphyton here don't get much light, so they are primarily filter feeders (non-photo). So they REALLY grow and position themselves to be able to intercept food particles in the flowing water.You'll sometimes see little tree-like arms or branches sticking out to get the particles; these are usually "forams", otherwise known as foraminifera. They require a lot of food particles in the water. Think of them as coral polyps without the coral.

Reef studies have shown that at certain depths, more of the filtering of the water comes from periphyton and benthic algae, than comes from the phytoplankton which filters the deeper water. And in streams, almost all the filtering is done by periphyton because the water is so shallow. So, what you have on rocks that are "mature" or "established" is a well-developed layer of periphyton (and all the good natural things that comes from it, like nutrient absorption and food generation). They have nice colors too.

This is why mandarin fish can eat directly off the rocks of an "established" tank (tons of pods grow in and consume the periphyton), but not on the rocks of a new tank. Or why some animals can lay their eggs on established rocks, but not new ones. Or why established tanks seem to "yo-yo" less than new ones (the periphyton is a giant, self-adjusting filter). Even tangs can eat periphyton directly when it's thick enough. Yes periphyton can also develop on the sand, but since the sand is moved around so much, the periphyton does not get visibly thick like it does on rocks. So thick periphyton on established rocks is your friend. And totally natural too. That's why there are no pure white rocks in natural reefs. Keep in mind though I'm not referring to nuisance algae on rocks; I'm only referring to the layer of coloring and textures that coats the rocks, and the little arm-like structures that stick out from under rocks.

But what happens when you "scrub all the stuff off your rocks"? Well, you remove some of the periphyton, which means you remove some of your natural filter and food producer. What if you take the rocks out of the water and scrub them? Well now you not only remove more of your natural filter and food producer, but the air is going to kill even more of the microscopic sponges. And what if you bleach the rocks? Well, goodbye all filtering and food producing for another year. It's an instant reduction of the natural filtering that the periphyton was providing. So it's best to not do these things at all.

However, what if you just re-arrange the rocks? Well, some of the periphyton that was in the light, now will be in the dark; so this part will die. And some of the periphyton that was in the dark will now be in the light, so it will not be able to out-compete some photosynthetic growth and thus will be grown over and will partially die too. And even if the light is the same in the new location, the direction and amount of water flow (and food particles) will change; forams and micro sponges that were oriented to get food particles from one direction will now starve. So, since the light and food supply is cut off in the new location, the filtering that the periphyton was providing stops almost immediately, due only to your re-arranging of the rocks.

Starvation takes a little longer. The periphyton organisms won't die immediately, since they have some energy saved up; but instead they will wither away over several weeks. So on top of the instant reduction in filtering that you get by just moving the rocks, you get a somewhat stretched-out period of nutrients going back into the water. And after all this, it takes another long period of time for the periphyton to build up to the levels it was at before: 1 to 2 years. Even changing the direction of a powerhead will affect the food particle supply in the area it used to be pointed at. This is why "mature tanks" take 1 or 2 years to develop.

So a good idea is to try to keep everything the same. Pick your lighting, flow, layout, and then try to never again change anything. In other words, treat your rocks just like the rocks on a reef. It's a different way of thinking, but you should have a stronger natural filter and food producer because of it.