The Nitrogen Cycle in Planted Aquariums

This post is not going to be perfect. It’s my understanding and learnings based on my experiences getting started with planted aquariums. Much of this is an over simplification, but it’s the mental model of how I think of my ecosystems.

One of the things that had kept me out of the water keeping hobby is the maintenance. I didn’t realize how much interesting science and problems there are to solve. I’ve thoroughly enjoyed my time in this so far. I love talking about it, and just like everything else I do, I’ve found some interesting problems to solve for.

Hold on to your butts!

Starting with water parameters. If you talk to anyone about a problem with your tank, they are going to ask, “what are your water parameters”? Water parameters are what we use to know how balanced the nitrogen cycle is. The most important parameters for the cycle are, ammonia (NH3), nitrite (NO2), and nitrate (NO3). But they also include things like pH, chlorides/chloramines, etc.

View fullsize

The nitrogen cycle starts with ammonia which is converted to nitrite which is converted to nitrate. Then it stops - the nitrates stay in the water until they are removed. Over time, you’ll get a build up of nitrates and everything will die. Not ideal. Actually, if you have a sudden spike of any of these chemicals, you risk losing everything in your ecosystem. The quickest way to deal with the spike is generally a water change (50% or so). I’m really shooting for an ecosystem that doesn’t need frequent water changes.

How do we do that? By completing the cycle and getting rid of the nitrates - WITH PLANTS!

Let’s talk through what is converting these chemicals. Ok - so surface in your tank is growing bacteria on it. This does not include algae (which is an entirely different post). There are two types of bacteria that are in the tank, Nitrosomas Bacteria, Nitrobactor Bacteria.

Fish, like most living things, create waste in the form of ammonia. ammonia is also created from decaying matter and uneaten food. Nitrosomas bacteria convert the ammonia to nitrite, how? IDK. So now we have nitrites.

Nitrobactor bacteria is responsible for converting the nitrite into nitrate. Awesome. Now what? I’m using live plants to consume the nitrate. Side note, nitrate is common in most plant fertilizers.

There’s a complication that needs to be worked out here. The bacteria that is keeping the water safe for fish need as much surface area as we can provide so they can keep up with the ecosystems bio load. There are some options for increasing the surface area available to bacteria.

• Aquarium gravel

• Sponge filters

• Canister/Hang on back filters with biomedia

• Sump tanks

• and… PLANTS

For now - I’m trying to keep things simple and reduce the number of failure points and moving parts, etc. Having heavily planted tanks provides enough surface area for bacteria that so far, I’ve only needed small sponge filters to keep the water visibly clean. I’m mostly using low light plants that don’t need CO2 injected into the water.

One last thought on bacteria. They need the water around them to be moving ever so slightly. Use air pumps to drive sponge filters and air stones to keep the water moving. Try to prevent areas in the tank with no water movement. I’m also using snails and shrimp to keep surfaces clean. If too much algae is growing on the plants, glass and substrate, the water gets slowed down and the bacteria can’t process fast enough. Then there’s an ammonia spike.

Have fun - reach out if you have any questions! I love talking about this stuff - we can learn together!

Happy Hobbying!

Greg’s Rules for the Nitrogen Cycle

SUBJECT TO CHANGE WITHOUT NOTICE

Ammonia is not zero

• Remove any visible decaying matter

• Immediate water change (25 - 50% depending on severity)

  • Vacuum gravel

• Look for algae problems

  • Reduce lighting

Nitrite is not zero

• Water change (10 - 25% depending on severity)

Nitrates over 50 ppm - having some nitrate are good and needed for plant growth

• Water change (10 - 25% depending on severity)

• Consider adding / propagating plants

• Increase lighting

Current Hobby Room Display Tank Setup

• 20 Gallon long tank

• Nicrew SkyLED Plus

• 100W Heater

• 2 Sponge filters

• Dragon stone

• Driftwood

• Plants

  • Wysteria

  • Anubias

  • Java Fern

  • Water Sprite (I think)

  • Pothos (growing out of top of tank)

• Animals

  • 3 Dwarf Apistogramma Cacatuoides

  • 12 Glow Light Tetra

  • 8 Ember Tetra

  • 6 Pygmy Corydoras

  • 3 Endler’s Livebearer

  • 4 Nerite Snails

  • 1 Assassin Snail