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 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.