Using Seaweed to get rid of nuisance algae in your aquarium or pond

[SantaMonica]

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 the 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) 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 Iron too.

Sounds like an ideal filter, right? Remove 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 version of this neat filter (for fresh or salt) in the coming posts.

 

[SantaMonica]

Using Seaweed to get rid of nuisance algae in your aquarium or pond

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 "eat" the CO2. What organisms might these be? Algae, of course. Or more specifically Photo-Auto-Trophs (photoautotrophs), meaning they get their food (carbon) by themselves (auto), without needing to eat other animals, and they do it 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 all shallow rivers and streams), 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 shallow 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 easy to understand 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. Water that is near the seaweed (say, 10 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 puts the seaweed more near to the "oven" of the water surface where the air is. This "near-ness" of air to the seaweed is what makes things work for our filtering needs.