Basics of Planted Aquariums

I got our planted Spec V started about three years ago. Along the way, I’ve learned quite a bit about planted aquariums (I still have so much to learn) and I wanted to try and summarize the basics.

What Plants Need:

Aquarium plants have a few basic needs. Good thing we generally have water covered; beyond that, for photosynthesis to occur, plants need nutrients, light, and Carbon Dioxide (CO2).

I will use the word ‘Fertilizer’ interchangeably with ‘Nutrients’. Fertilizers refers to the minerals that plants need to survive and thrive. These include nitrogen, potassium, iron, and other trace elements.

Light should be easy to understand, although it gets complicated when it comes to understanding how much (what intensity) and how long (duration of lighting period).

Understanding CO2 and how that translates to healthy plants gets more complicated, being that it is invisible, and not easy to quantify.

Plants – Slug-Bug or Ferrari:

So we understand what plants need (fertilizer, CO2, Light) but where things get complicated is deciding how much of those three needs to provide and how to provide it.

When you go shopping for plants, they are often divided into categories of low light, medium light, and high light. The titles tell you what they need for lighting; however, I like to think of plants in terms of ‘speed’. High light plants are ‘fast’ as in fast growing, like a Ferrari. They have a high ceiling for the rate that they can photosynthesize. If you provide an abundance of all three of their needs (light, CO2, fertilizers) they will grow very fast and consume CO2 and fertilizer at a high rate. Conversely, low light plants are ‘slow’; even with excessive light, fertilizers, and CO2 they have a low rate of growth and will not consume much fertilizer and CO2 (relative to ‘fast’ plants).

low light planted aquarium

Examples of low light plants are annubias, vals, mosses, and some cryptocorynes. I have a hard time separating medium and high light plants and tend to think of them as the same group. This is simply because many of the high light plants also do well in medium light; they just grow slower. Medium to high light plants include some cryptocorynes and includes many of the carpeting plants, such as dwarf baby tears (HC) and hair grass.

Lighting – Get Your PAR On:

As I have alluded to already, you need to provide your plants with an intensity of light that meets at least their minimum needs to survive and thrive. Notice my careful wording here as there is a range of light intensity that any plant can handle. Low light (slow) plants can get by with very low light intensities but may be fine with excessive light. Some fast growing plants do fine in medium light but can really thrive (fast growth, better coloration) in high intensity light.

Light intensity, in the aquarium hobby, is measured in PAR. I’m not going to get into any scientific explanation of what PAR is, just know that it is light intensity delivered to the plant’s level. A given light fixture’s PAR level (intensity of light provided) will vary depending on the distance the light is from the plant. Carpeting (short) plants in my Fluval Spec V would be at around 10″ below the surface of the water.

I now have a Seneye PAR meter that I use to review planted aquarium lights – I discuss more about PAR measurements on that page.  As an example, the light we currently use, the Finnex Planted+ 24/7 HLC, provides measured 127 PAR to the center of the tank at the substrate surface.


Lighting intensity, similar to plant light needs, is traditionally divided into low light, medium light, and high light. Opinion varies, but I like to think of the following ranges:

  • Low Light Level: 15-30 PAR
  • Medium Light Level: 30 PAR to 50 PAR
  • High Light Level: 50 PAR and above

Low light plants will do best if provided with PAR values in the range of 15-30. Medium and High light plants need PAR values of at least 30, with higher PAR values potentially leading to ‘faster’ growth.

As I will discuss shortly, more is not always better when it comes to lighting. Providing too much light can often times result in an algae farm and much frustration.


Compared to lighting and certainly CO2, fertilization can be easy to accomplish, but difficult to understand and plan for. There are many solutions for providing the plants with the minerals that they need, such as Seachem Flourish or other ready made liquid fertilizers, as well as dry fertilizers.


dry fertilizers for planted aquarium EI dosing: potassium nitrate, potassium phosphate, CSM + B

The methodology that I believe in strongly is dosing dry fertilizers using the EI (Estimative Index).  I have an article on dry dosing that explains where to get dry fertilizers and how to dose. The basic premise of EI dosing is to provide the plants with more fertilizer than they need and then ‘reset’ the tank with weekly 50% water changes. Dry dosing usually includes: Potassium Nitrate (KNO3), Potassium Phosphate (KH2PO4), Potassium Sulfate (K2SO4), and Trace elements (using a product called CSM + B or similar).

CO2 – A Plant’s Gotta Breath:

Many of the most respected aquarist point to CO2 as being the key to successful plant growth and keeping algae at bay.

CO2 is necessary for photosynthesis to occur. During photosynthesis, all plants consume CO2 and give off oxygen. CO2 is naturally occurring in water exposed to atmospheric air.  Without any additional intervention, it will be at around 4 parts per million (ppm) in an aquarium.  Plants may need many times more than that to grow at their full potential.

For those that are looking to increase CO2 that is available in the water column, the first step is often dosing a liquid CO2 substitute, like Seachem Flourish Excel.  This product does not directly increase CO2 concentration in the water, but it makes available additional carbon to the plants.  This is helpful in bridging some of the deficiency in available carbon, but it is very limited. You can’t manage a high light and fast growing plant selection with only carbon additives.

Carbon additive for planted aquariums - Seachem Excel

After CO2 substitutes like Excel, you move to injecting actual gaseous CO2.  One method involves gathering CO2 formed as part fermentation and injecting that into your tank.  This is commonly known as “DIY CO2“.  It is thought to be easier than pressurized CO2 (discussed next) but I’m not convinced.  It involves changing out sugar/yeast combinations when they are exhausted.  It can be messy and it can take up lots of room if you are dealing with more than one fermenting chamber.  It is always on (even when the lights are off) and it tends to not be consistent with delivery quantity / pressure.

Finally, there is pressurized CO2 systems.  These involve taking a pressurized tank of CO2 and using that to disperse into the tank.  These are thought of as being complex and expensive.  As I have found in getting my little paintball CO2 system going, they can be completed on a budget.  The advantage of pressurized CO2 systems are many: timed delivery (when paired with a solenoid valve), consistent delivery of CO2, and the ability to reach CO2 saturation levels as high as you need.

Managing Algae Means Finding Your Limiting Factor:

I think anyone who gets into planted aquariums has the same vision: perfectly clear water, lush and healthy plants – an oasis of beauty inside a glass canvas.  Unfortunately, that perfect vision often gets disrupted by the reality of algae infestations and unhealthy plants.  I have experienced this to varying degrees with our tank.  To a certain extent, these struggles are inevitable, but I have come to understand there are methods to almost eliminate the problems of algae and unhealthy plants, but it takes an understanding of how those three necessary elements (light, fertilizers, CO2) work in an aquarium.

Not everyone agrees, but I have come to believe in the theory of resource utilization expressed by Tom Barr. Rehashed in my own way, it stands on two understandings.

The first concept is basic: If you provide your aquarium plants with everything they need to grow to their potential, everything will work out in regards to balance and overcoming algae.  The problem of algae in your tank becomes a situation where you can be come fixated on the algae, constantly trying to either add something or take something away that will kill the algae. In a short term outbreak, this mentality is sometimes necessary. However, it is short sighted and misses the real goal, which is healthy and thriving plants.  Make decisions based on what the plants need to grow to their potential, and algae problems will often take care of themselves.

The second concept expands on the first and goes deeper into what the plants need and, more specifically, what is their limiting factor. Simply stated:

Your plants will only grow to the potential of what you are providing.  If there is any deficiency in what is provided, the plant growth rate and health will be limited by that deficiency.   

Let’s look at an example in this diagram:

Planted Aquarium Diagram - Medium Light with No CO2

This describes our tank over the past few years.  It was stocked with low to medium growth plants. Lighting was from a Finnex Planted + fixture that results in medium to high light levels.  I did dose Seachem Excel to help with the plant carbon needs. Fertilizers was with EI and used a dosing regimen for a low light / low tech aquarium.

The result was a tank that had good growth and fairly healthy plants, but had more algae than I wanted. I hope you can see from the diagram what was the cause.  The fertilizers added exceeded the growth potential of the plants, so that was not the limiting factor. Light was in excess of the plant ‘s growth potential, so that is not the limiting factor.  The problem was CO2. Being that I was not using pressurized CO2, saturation would be no higher than 4 ppm.  The plants were limited by CO2 and therefore never grew beyond this limiting factor.

Anytime you have a deficiency that results in stunted growth of plants, algae will swoop into the gap and take over. Algae is more efficient and can thrive in these areas of deficiency.

See the diagram below for what happens to the example above if you add pressurized CO2.

Planted Aquarium Diagram - Medium Light with CO2

Deficiencies are removed and the plants can now grow to their full potential.  Algae now has no resources remaining to thrive as the plants are using them all up.

Light – The Gas Pedal to Your Aquarium:

Light is somewhat unique from CO2 and fertilizers in that you can’t simply provide a surplus in whatever quantity you wish without repercussions.  The light intensity suitable for your plants can fall in a wide rang; your choice of where you fall in that range depends on a few factors.

First of all, remember how I described plants as ‘fast’ and ‘slow’ growth. Let’s run with that analogy and think of light intensity as the throttle of your planted aquarium.  You can choose to have a very high intensity light (pedal to the floor), or a medium intensity light (slow that tank down).  If you choose to run on the ragged edge with a ‘fast’ tank, you can end up paying the price if something becomes deficient (CO2 bottle runs out, forget to dose frets, etc.).  You can use a lower light level, have slower growth (less trimming) and run less risk of algae.

In addition to light intensity, we have another variable in duration, or how long you choose to have your lights on every day. When I started out, I wondered about the following:  Is running a 15 par light for 10 hours the same as running a 30 par light for 5 hours?  The answer is No.  Plants need a minimum amount of energy to start and maintain photosynthesis; this amount varies based on the ‘speed’ of the plant (low light or high light).  I like to think of it like starting a fire.  I can apply a low level of heat to some paper and never have it ignite.  If I pass the ignition temperature for that paper, then it starts to burn.  In the same way, you have to exceed the plant threshold of intensity to get photosynthesis going.

You can vary light duration and see how it affects your tank.  It does seem that less than 4 hours may not be adequate for plants to achieve a good photosynthesis cycle.  Conversely, beyond 10 hours plants may not be able to sustain strong photosynthesis; during the excess time the lights are on, plants won’t be making use of nutrients and CO2, but Algae will!

A 6-8 hour light duration is a great place to start.  Less can often times be better than more.

Defining Your Priorities and Goals:

I hope the information here helps you to visualize what plants do to grow in an aquarium and also helps to understand how Algae can be limited.  For those getting into the planted tank hobby, the most important thing I hope you get out of this is to realize the need to plan and set goals while understanding limitations.

Starting out a few years ago, I knew I was not ready for the complexity and cost of a pressurized CO2 system.  I tried my best to work within those limitations by choosing low to medium light plans. I utilized Excel and EI dosing to try and maintain the plant nutrient and CO2 (carbon) needs, and  I used a light schedule to try and limit algae growth.  Generally, this was successful.  However, the limitation of not using pressurized CO2 highlighted limits to this type of system; namely, a limited selection of plants and some battles with algae.

Now, several years later, my goals have changed.  My desire for using a more broad selection of ‘fast’ plants and my desire to limit algae has led me to try and remove the limit for pressurized CO2.  Again, this is a case where my desires are expanding my limits.

I have just now installed our pressurized CO2 system and have completely rescaped the tank with a new selection of plants.  I will be adding new articles about this transition in the future.

Additional Resources:

In the interim before I can roll out additional articles about EI dosing and pressurized CO2, I’d like to share a few links that have been useful to me:

  • The Barr Report:  This website is by the aforementioned Tom Barr.  If you browse through this forum, you will find information on EI dosing, CO2, and other aspects of planted aquariums.
  • Sudeep Mandal – Low Tech Planted Aquarium: This site breaks down running a low tech aquarium and is based on Tom Barr’s methodology, but it is more concise and easy to understand.  I used this page heavily in planning for our initial low tech setup.
  • Sudeep Mandal – Low Tech Planted Aquarium with Excel Dosing:  Same site as the link above, same theories, but he details methods for also dosing Seachem Excel.
  • CO2 art and CO2Supermarket:  Both of these retailers have many (if not all) of the components you need to assemble a Pressurized CO2 system.  I used CO2 Supermarket and they were excellent – I got a paintball setup going for much less money and pain than I ever thought possible.

13 thoughts on “Basics of Planted Aquariums

  1. Thank you for your website. I currently have a betta in one of those 3 gallon tanks that has plants growing on top of it to complete the ‘cycle’ (no live plants inside it, just fish store gravel) but it was a little underwhelming so I just purchased a Fluval Spec V (which I think is how I ended up at your website, looking for reviews)

    Your site has been a great help since so much of your planning is based around that same tank. I’m going to add live plants to the new tank so I was wondering what your suggestion would be to start the tank up right. I have been looking at the Barr Report and am intrigued by the dry start method he discusses there though maybe not so much on the length of time it takes before you can put the fish in (at least a month) What approach would you recommend I take to cycle a brand new Spec V? (I have ordered some UP Aqua Sand via one of your affiliate links so hopefully you got a kickback for that) Are there any specific plants you would recommend in a new tank (and how many?) And do you generally order them online or do you get them at local fish stores? I live in Los Angeles and there seems to be a tropical fish store on every corner here.

    In addition to my existing betta I was going to grab some shrimp and maybe some tetras. Is there a general number of each (like 4 tetras and 4 shrimp?) that the Spec V generally can support? I read about the 1 gallon per inch of fish thing but I’m not sure how shrimp play into that.

    Also would you recommend I just jump into CO2 or is it worthwhile to start without it?

    I guess basically I’d just like a summary of how you’d start a new Spec V now knowing everything you’ve learned over the last few years, what technique to cycle, which plants and what amount to start with and which fish.

    Thanks again, this website really has been a great help.

    1. Keep researching and you will get there. Dry start is intended for certain types of plants; generally it is used for ‘carpet’ plants. I have never done it.

      The approach I would take to cycle an aquarium would be to do a fishless cycle.

      Plant suggestions depend on the many factors I talk about above: high light, low light, co2 injection, etc. Nail those points down first, then research accordingly. I have gotten all my plants online and that has worked well for me.

      Your betta might eat shrimp. See this page for thoughts on stocking your Spec V.

      I can’t say if you need to jump right in with CO2. It’s definitely worth it to start without it; without CO2, think about using lower light intensity and pick plants and nutrients to suit that light intensity.

      I can only give you a summary of how I started and how I got to where I am. No use following my path (that would include lots of mistakes) – make your own path and have fun.

      You are very welcome. I will keep trying to add articles to answer many of the questions you are asking.

  2. So does surface disturbance increase co2? Can you point the pump nozzle straight up and increase surface disturbance therefore increasing co2? I just got my spec v (your website has been invaluable, major props) and am going to go low and slow to start out and I don’t want to spring for the co2. Please tell me if I go slow enough, I don’t need co2. Thanks.

    1. Sorry to say, surface agitation increases O2 levels, but does not significantly increase CO2. This is because atmospheric air is only about 0.03% CO2.

      If you don’t want to use CO2 then don’t bother with it. I had our tank with no CO2 for 3 years and it did wonderfully. Just pick a light intensity a bit lower (and maybe a shorter duration), and pick plants that go well with lower to medium light.

  3. I just got done setting up a plantic spec v for fishless cycling only to realize that I do not have ammonia. Can I cycle it by just adding a piece of fish or shrimp as a source of ammonia in the meantime while I get my hands on some pure ammonia.


    1. I have read that will work, but have not tried myself. Go for it and see what happens.

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