Planted Freshwater Aquaria

Written by Fred Chen, November 19, 2002

A tropical freshwater aquarium doesn’t look quite right to me unless it has a lush growth of live aquatic plants. The fake plastic or silk varieties just don’t cut it for me.  It has to be the real thing.  I’m hoping that you also think the same way.  If so, then there are a few things you need to know in order to grow aquatic plants successfully in your aquarium.  It’s really not that difficult once you take the time to find out what aquatic plants need in order to survive and flourish.  There's some science involved, but you don't really need to know all the details to make it work for you.  For example, you don't need to know how an internal combustion engine works in order to drive a car.

While most beginners in this hobby tend to focus on the fish first, I think it’s far less work in the long run if you focus on the aquatic plants first.  Then once the plants are growing well, go and get your fish.   Of course, if you plan on having an African cichlid tank, then live plants are probably less suitable because of a cichlid’s propensity to uproot everything in the tank.  Then, you should probably focus on the fish instead of the plants.  But for many species of fish, aquatic plants and fish make an almost magical partnership in any aquarium.

To grow strong, healthy aquatic plants in an aquarium, you will need to pay attention to the following three basic, but very important things (in order of priority):  1)  Lighting; 2) Carbon Dioxide; 3) Nutrients; and 4) Substrate.  These items will be discussed separately in the following sections.  

After you have properly addressed these items in your aquarium, you can now turn to your creative side and put your work of art together.  This process is called "aquascaping" and is an entirely different topic of discussion.

LIGHTING

Plants need lots of light in order to photosynthesize properly and produce the energy they need to grow and reproduce.  Most light canopies that come with aquarium tanks typically do not provide enough light for proper plant growth.  However, they always seem to provide enough light for that unwanted algae!

I will focus only on fluorescent lighting since that’s only way to go with planted aquaria.  Incandescent lights are just too inferior.  The general rule for lighting is to provide 2 – 3 watts of light per gallon for 10 – 12 hours per day.  It’s best to use a timer to deliver the light at regular times during the day.  My timer is set to turn on the lights at 09:00 and to turn them off at 21:00.

There are some newer fixtures that incorporate the use of compact fluorescent tubes instead of the regular fluorescent tubes.  These compact tubes are costlier than the regular tubes, but they do provide a brighter light for the wattage.  Fluorescent fixtures and tubes sold by aquarium stores tend be quite costly (up to $45.00 CAD each).  If you are on a tight budget and do not mind the looks of your aquarium fixture/hood too much, then you can pick up industrial fluorescent fixtures and standard fluorescent tubes instead from the local hardware store.  It’s best to get fluorescent tubes that approximate the light temperature of daylight (6,500 ^oK).  In aquarium stores, you can get all kinds of different light temperatures for various applications.

It’s also a good idea to have some sort of glass cover between the lighting fixture and the water in the aquarium.  Although, the humidity doesn’t appear to affect the operation of most fluorescent lighting fixtures, you certainly don’t want to knock a live electrical fixture accidentally into water!

CARBON DIOXIDE (CO₂)

Alkalinity is generally known as the buffering capacity of the water.  This buffering capacity is the ability of the water to resist changes in pH.  In general terms, water that has a low alkalinity is known as being “soft,” and water that has a high alkalinity is known as being “hard.”  Alkalinity test kits measure carbonate (CO₃^2-) in units of KH, or degrees of hardness.  This is not to be confused with DH, which is also degrees of hardness, but is determined based on the concentration of dissolved magnesium (Mg²⁺) and calcium (Ca²⁺) ions in the water.

Once you have the pH and Alkalinity results, you can use the table below to determine the concentration of CO₂ in your water.   Note that this table only works if you do not have any phosphate in the water since the alkalinity test kits cannot compensate for this.

 Table 1.  Determining CO₂ Using KH and pH Values

Do-It-Yourself (DIY) CO₂ System

There are lots of good do-it-yourself (DIY) designs on the Internet for constructing your own CO₂ generators and reactors using a mixture of yeast, sugar, and water so I’m not going to duplicate the information already available.  However, I believe the best construction plans are found on John LeVasseur’s website at http://www.qsl.net/w2wdx/aquaria/diyco2.html.  His website is well written and referenced.  I particularly liked the well laid-out diagrams, photos, and the links to various parts suppliers.

CO₂ systems for planted aquaria are closed systems; therefore, the CO₂ is always under pressure while the yeast is still active.  Pressure-release systems should be a part of any DIY system in case there is a buildup of gases due to an unforeseen airline blockage.  Without some sort of pressure-release system installed, you risk an explosion resulting in bits of broken generator bottle with a sticky, smelly mess of yeast, sugar, and water all over the room.  For my own CO₂ generator and reactor, I incorporated many of the items described on John LeVasseur’s website, with a few small modifications due to certain items I already had available at my disposal.

Fittings.  I like the practicality behind a modular design so I incorporated Mr. LeVasseur’s idea of using special 3/32” ID bulkhead fittings, normally used in the fuel lines of remote-controlled (R/C) aircraft, for the cap on the generator bottle.  These bulkhead fittings provide a very nice seal when used with common ¼” airline tubing.  These fittings are manufactured by Fourmost Products (Part No. FOR 121) and cost about $5.69 CAD (about $3.60 USD) per package of two.  The fittings also come in different specifications to accommodate various tube sizes.  The bulkhead fittings can be found at R/C aircraft hobby stores.   

Most DIY plans simply tell you to drill a hole through the cap for the airline, and to seal any gaps with silicone for an airtight seal.  Typically, the cap/airline junction is the structural weak point in many construction designs.  The bulkhead fittings make all your connections neat and tidy.  Besides, the hole-and-silicone method looks messy and makes it more troublesome when you have to swap generator bottles.

Installing check valves on the airline tubing somewhere along the line to prevent any accidental siphoning of the aquarium water back into the CO₂ system is also a very good idea.  I installed my check valve on the section of tubing between the reactor and the gas trap (more about gas traps later).

Generator.  A CO₂ generator is simply a vessel that contains the mixture of yeast, sugar, and water, allowing it to react and produce CO₂.   This vessel can be any clear container which can be sealed, preferably with a screw-top cap.  Most designs incorporate the use of 2-litre plastic pop containers as the generator because they are readily available, and they are designed to hold pressurized, carbonated beverages making them rather ideal for the DIY project.  However, I opted to use 2-litre glass bottles used by chemical manufacturers for storing concentrated mineral acids.  Most people generally don’t have access to these types of bottles, but since I work at a laboratory, I have a ready supply of good, used bottles.  These bottles are simply recycled or thrown out anyway.  I simply rinse these bottles out with copious amounts of water before bringing them home (this is important because the acid is very corrosive and any residual acid can ruin anything it comes in contact with).  These glass bottles to be far stronger than the standard plastic 2-litre pop bottles, and their base is more stable and less prone to being accidentally knocked over which is an important feature when you’re dealing with liquids.  I also employed a gas trap in my design which also serves as a bubble counter (more about gas traps in the next section).

Gas Trap.  The main purpose of the gas trap is to ensure that only CO₂ reaches the aquarium.  Since the yeast/sugar mixture is under pressure and tends to get messy, it can sometimes travel down the lines and into the aquarium, fouling the water.  The gas trap prevents this from happening since anything coming from the generator must first pass through the water in the trap before proceeding to the reactor in the aquarium.  With everything working properly, CO₂ will be seen bubbling through the water in the trap as it continues on to the reactor.  The bubble rate in the gas trap can be used to measure the amount of CO₂ produced, and a decrease in the rate signals when to change to the yeast/sugar mixture in the generator bottle.  I generally change the mixture for my 33-gallon aquarium when the bubble rate falls below 1 bubble per second.  The rate for your aquarium will be different depending on how much CO₂ your aquarium needs.

The gas trap was constructed by drilling two 3/16 inch holes into a No. 6 (1 - 1½ diameter) rubber stopcock (a suitably sized cork will also do), and feeding two sections of ¼” rigid airline tubing through the drilled holes placed at two different depths: one set below the surface of the trap’s water line and the other set about ½” below the bottom of the stopcock.  For the container of the gas trap, I used a 500 mL Erlenmeyer flask.  I then filled it with about 100mL of water to serve as the bubble counter.  I used the flask because it happened to be available to me, but any suitably sized bottle/cork combination will do.

As mentioned earlier, it is important to incorporate some sort of pressure-release system for safety reasons.  The gas trap also serves in this capacity.  If any excess gas pressure builds up in the system due to a blockage, the stopcock simply pops off the neck of the flask expelling the gas harmlessly into the room.   Just be careful not to fit the stopcock or cork onto the neck of the gas trap too tightly; otherwise, it won’t come off easily which negates the purpose of having a trap.

Reactor.  The purpose of the reactor is to create a high rate of CO₂ dissolution into the water.  Omitting the reactor in a DIY design and simply bubbling the CO₂ directly into the water using open airline tubing or bubbling it through an airstone will also work, but the rate of CO₂ dissolution will be much lower since most of it will just bubble to the water’s surface and dissipate into your room.  Since we’re going through all the effort of making CO₂, we might as well as make the best use of it and not waste it.

Construction of the reactor is simpler if you incorporate a plastic gravel cleaning tube (commonly used for cleaning aquarium gravel) into the design since it already includes a connection for ½” tubing on the top.  However, my reactor chamber was constructed using a clear plastic cylinder, about 1 ½” in diameter and 10” in length.  The cylinder was modeled after the plastic gravel cleaning tube, but without the added cost.  The cap for the cylinder came from a 1.89 L juice container which happened to be the right size for the plastic cylinder I was using.  The cap was secured to the cylinder using several wraps of Teflon plumber’s tape around the neck of the cylinder.  If you're using a gravel cleaning tube, you don't have deal with all this.

Two holes were drilled into the cap on my reactor: one hole to allow for an 6” section of ¼” rigid airline tubing which is connected to a fine-mist, glass-bead airstone manufactured by Kordon (Part No. 62503), and the other hole for a common ½” plastic bulkhead fitting used in household plumbing. The holes in the cap were drilled slightly smaller than needed to ensure a tight fit, and to avoid the need for using silicone for caulking or sealing.  The Kordon airstone sells for about $2.99 CDN ($1.90 USD).  It is costlier than the common varieties of airstones, but Kordon airstones are more resistant to the acidic environment associated with a CO₂ system.  You will come to appreciate it once you've had to take apart your reactor in order to replace a cheap airstone.

The bottom section of the reactor is plugged with an ordinary nylon kitchen scrubber which was cut to size so it would occupy about 1 ½” of the bottom section.  This part of the reactor is designed to keep the CO₂ bubbles from getting blown out the bottom, but allow CO₂-saturated water to exit the reactor..

The top section of the reactor is connected to a powerhead.  Powerheads are often used for undergravel filters to pump water into the reaction chamber.  I am using a Maxi-Jet PH 400 powerhead manufactured by Aquarium Systems for my 33-gallon tank.  Check the capacity of the powerhead before buying one to make sure it's the right size for your tank.  

I installed a foam pre-filter installed over a 2” section of ½” rigid tubing connected to the intake of the powerhead.  This filter prevents debris from getting sucked into the powerhead and blown into the bottom of the reactor.  The foam pre-filter also serves as a secondary filter for the aquarium. 

Yeast Mixtures.  There are several different CO₂ yeast recipes available on the Internet.  Keep everything clean and aseptic as yeast does not like to compete with other bacteria.  The recipe I use is as follows:   

NUTRIENTS

Aquatic plants need nutrients such as nitrate nitrogen (as NO₃^-), phosphorus (as PO₄^-), potassium (K⁺), and certain trace elements such as iron.   You can purchase pre-made solutions at the local fish store from a variety of manufacturers, or you can make your own from powdered chemicals.  This homemade solution is often called “Poor Man’s Dosing Drops” or PMDD (sorry, there's no poor woman's dosing drops...forgive me for not being politically correct).  The PMMD recipe is as follows:

The chelated micronutrient mix is available in Canada as plant-prod which is manufactured by Plant Products Co. Ltd. in Brampton, Ontario (available in the USA as Plantex).  A 100-gram quantity of plant-prod is about $4.95 CAD ($3.10 USD).  Many of these chemicals can be purchased from your local hydroponics store.  

plant-prod Chelated Micronutrient Mix (Guaranteed Analysis):

Keep the PMDD solution in a dark bottle and store in a cool, dark location.  The addition of hydrochloric acid (also known as muriatic acid) to the solution (optional) is to deter the potential growth of mold.  The PMDD dosage will depend on the number of plants and fish present in the aquarium, how often the fish are fed, the lighting conditions, the background levels of nutrients, etc.  For my 33-gallon aquarium, 2 mL every 2 – 3 days seem to work well.  When adjusting dosages, make sure to do it gradually over several days to avoid shocking the plants.   Measure the nitrate and iron levels in the water to determine if you need to change the dosage.  The ideal nutrient levels for nitrate are 3 – 5 mg/L.  For iron, it's 0.1 mg/L.  You may need to make a new PMDD solution with different chemical ratios if the optimum levels cannot be reached after adjusting the dosages.

You may notice that there is no phosphate in the PMDD.  Phosphate should be avoided as a nutrient since it tends to encourage the growth of algae.  Phosphate will also mess up the determination of CO₂ if you're using KH test kits (see Carbon Dioxide section).  There usually is enough phosphate coming from fish waste and the fish food, so not supplementing the water with phosphate shouldn’t be a big problem.

For lots more information on PMDD, visit the Practical PMDD Information (Sources and Doses) on The Krib website.

SUBSTRATE

In planted aquaria, the substrate or gravel, is used to provide a medium for anchoring aquatic plants and to supply nutrients to the plant via the root system.  Some epiphytic plants, such as Java Ferns and Anubias, don’t really require gravel and can anchor themselves to submerged wood and large stones.  They obtain their nutrients entirely from the water.   The substrate also provides a decorative feature to the aquarium, and a reference point for the fish.  In keeping these points in mind, the proper substrate is important for a planted aquarium.

There is a great variety of different substrates available on the market today.  Most planted aquaria are designed to appear as natural-looking underwater environments, so the choice of substrate should reflect this.  For that reason, the use of highly coloured (e.g. blue, green, pink, etc.) often found in some “novelty” aquaria will not be given any consideration at all.  Just for kicks, some examples of coloured gravels can be found here.   

When selecting a substrate, make sure it is intended for aquarium use.  For freshwater aquaria, make sure you stay away from mineralized gravels that can potentially leach metals in the water.  Also, stay away from limestone and crushed shells as a substrate as these materials can release calcium carbonate into the water and make the water hard over time.  Before using any new gravel, make sure you rinse it with lots of water to remove any dust and loose dirt even though the package may say it’s already prewashed.

I use a natural-coloured aquarium gravel consisting of various particle sizes with the largest being ¼” in size.  I mix this gravel at a ratio of 50:50 with Flourite, a product distributed by Seachem.  The cost for a 7 kg bag is about $29.99 CDN ($18.75 USD; however, it can be found in the USA at much less than this).  Flourite is a porous clay gravel which has a high cation exchange capacity and is high in iron.  It is mined in the tropics in fluvial areas that are devoid of soil nutrients.  Flourite can also be used as a substrate on its own; however, I prefer the look of a gravel/Flourite mixture because it is not as monotonous as Flourite on its own.  Flourite comes in either dark Flourite (a dark brown colour) or Flourite Red (a reddish-brown colour).  Personally, I prefer the dark brown colour because it makes a very nice mix with the other gravel I use.  The general rule for the amount of substrate needed for an aquarium tank is about 1 lb of gravel per gallon.

Another substrate I have considered is Laterite, a product distributed by First Layer.  From the literature, Laterite has similar properties to Flourite but tends to be messier to work with, and can cloud the water if it’s not covered with gravel first.  It is intended for use as the first layer, or bottom layer of a multiple-layer substrate.  The recommended amount of Laterite for an aquarium tank is 1oz. per gallon.  If you want clay to be a part of your substrate, Laterite is a good alternative to the more expensive Flourite.  Laterite is sold in 25 oz. and 55 oz. packages and costs about $13.99 CAD and $24.99 CAD, respectively.

When I laid down the substrate in my aquarium tank, I sloped it from back to the front.  In my 33-gallon tank, this resulted in 5” of gravel in back and 2 ½” in the front.  The front should have a substrate depth of at least 2” to allow enough gravel for the aquatic plants to anchor themselves.  When filling the tank with water, place a 10" overturned dinner plate on the gravel and pour the water onto the plate to disperse the downward force of the water.  Fill the tank to about a third to a half with water before it's safe enough to remove the plate.  You are now ready to begin the next phase of your planted aquarium which is called, "aquascaping."  To find out more about aquascaping, please read my article on the subject.