Aquatic Plant Q&A
Anwers to your questions are available on the following plant topics:
``What do you absolutely need to grow plants?''
Successful plant growth requires a balance of light, nutrients, trace elements,
and carbon dioxide (CO2).
The light should be provided in a spectrum the plants can absorb, must
be of great enough intensity to keep the plant alive, and should be
on 10-14 hours a day. Most nutrients are supplied by
fish waste. Some trace elements might be supplied by your tap water,
but are more consistently obtained using commercial trace element mixtures. CO2
is supplied partly from the air and partly by your fish, but can be enhanced
by injecting it from an external source (for example, a compressed bottle).
If your plants
have a deficiency of even one of these factors, their growth will be
limited. (Don't panic about this; most of us don't need optimal plant growth.)
Overabundance of one factor over another may cause problems, such as
plant malnourishment, undue algae growth or toxic buildup.
Each ingredient will be discussed in detail in the following sections.
``My friend grows plants beautiful plants and doesn't do high-tech
stuff like CO2 or fertilizers. Is it really necessary?''
The quick answer to this is no. It is completely possible to
grow plants using basic tank equipment, either by chance or by patiently
learning through trial-and-error. This is accomplished by slight modification
of the basic equipment and usual fishkeeping practice.
High-tech gadgetry, however, can remove much of the guesswork
by allowing you to better control each of the four ingredients.
We should also mention that the term beautiful is
a bit subjective here; Many hobbyists achieve great success with ``easy''
plants and no special equipment, and this is perfectly fine.
But beware comparing this to a high-tech monger and their
ability to grow a wider variety of plants,
because they're really two different categories!.
New plants may have unwanted hitchers: snails, algae or disease.
Disinfection can help reduce their transmission into the tank, and can
be used to remove algae growths from established plants. Beware,
there is always a danger of going too far and damaging the plant
itself. Some popular methods:
(See the ALGAE SECTION of the DISEASE FAQ
for more algae-prevention
tips, and the SNAIL SECTION of that same FAQ
for snail prophylaxis.)
- A ten minute soak in potassium permangenate (pale purple) works well;
it is available in dilute form from Jungle products as "Clear Water".
Permangenate is particularly good for killing bacteria and pathogens.
A 2-day soak in 1 tbsp/gallon of alum (buy it at drug stores) is good for
killing snails and their eggs.
- If the plants are kept in a fish-free system for three weeks, parasites
like ich and velvet will die without their fish hosts.
- A soak in a 1:19 diluted bleach solution;
2 minutes for stem plants, 3 minutes for tougher plants. Make sure to remove
all traces of bleach afterwards by rinsing with water and dechlorinator.
This method can kill your plants, so use only as a last resort
against hell algae.
``Do I leave my new plants in the pot?''
Many aquatic plants are now sold in potted rockwool. Plants with delicate
roots, such as Cryptocoryne and Anubias, are usually
best left in the rockwool
wadding, especially if you have to move them around in the tank. Leaving
them potted also can reduce transplant shock; otherwise you must be
patient and allow the plants time to recover in their new substrate.
You can bury the pots
in your gravel to conceal them. Some folks like to cut away the plastic pot,
and just leave the plant in the wadding so it can grow out into the substrate.
``What kind of plants can I keep with fish X?''
These are essentially the same question, though asking the second one shows
you are a serious plant person.
You need to match the habits of the fish with the plant. Big cichlids that
like to dig should not be kept in a tank with rooted plants, though floating
(or ephiphytic) plants are fine.
Vegetarian fish should not be kept in a tank with plants
they like to eat, unless the plants grow faster than they destroy them!
Some algae-eating fish
also turn out to be plant-eaters too. In general,
try and learn the habits of your fish before you buy them and your plants,
and be prepared to find out what works by several trials.
``What kind of fish can I keep with plant X?''
Some fish that can be kept with virtually any plants:
danios, rasboras, gouramis, discus, bettas, angelfish (Pterophylum),
and in general most small fish.
``How much light do I need''
The ``classic'' rule of thumb for lighting is 2-4 watts of
fluorescent light per gallon (0.5-1 watts/l) for a tank of
normal depth, less than 24 inches (60cm). In reality, the issue is
clouded (so to speak) by the amount of algae and other particles in
the water and on the walls, what sort of reflector you have on the
light source, and how far away the source is from the tank. In
general, start with the guidelines, but be prepared to add more later.
For plants that demand medium to high light, most
people find they need at least two fluorescent bulbs of the length of
normal tanks (20-gallon (80l), two 24 inch tubes; 55-gallon (200l),
two 48 inch tubes). More detail can
be found in the later LIGHTING
``Can I grow plants with my single strip light?''
Yes, you can, though you are limited to the lowest-light plants
and will get very slow growth. Some of these include
Some of these plants, notably Cryptocorynes,
actually prefer lower light.
We should also mention that some people may have luck
with plants that normally prefer higher light, but the odds are that they will
grow slowly and stunted.
``What kind of bulb do I need?''
First and foremost, don't use incandescent lights; they generate far
too much heat and not enough light. Full-spectrum fluorescent bulbs
are ideal, since they duplicate the spectrum of the sun. These tubes
(``Vitalite'', ``Spectralite'') can be costly, at $8 to $20.
An inexpensive but effective alternative are tri-phosphor daylight
tubes such as the Chroma-50 or Design-50, which retail at $4-8; these
tubes do a reasonable approximation of sunlight.
Cheaper ``plant lights''
are also good, and may actually bring out your fish's color better.
Tri-phosphor bulbs (Triton, Tri-lux) are slightly more
powerful, but also more expensive than full-spectrum bulbs, and high-end
bulbs with internal reflectors (BioLume) are overpriced and
unnecessary. Other bulbs to avoid are standard cool-white tubes, and
``aquarilux'' tubes, designed to show off the fish and retard plant growth,
though some folks have had success with a mixture of cool white and
The term T-8 refers (usually) to high efficiency fluorescent tubes
installed in most modern office buildings, as opposed to the "T-12"
standard fluorescents. They are currently in vogue with some aquatic
plant keepers because of their relative inexpensiveness, longer life,
and high energy savings (consider that the ballast and tubes for a
4-tube 128-watt setup can be had for under $50). They can be
distinguished from their standard counterparts by three things:
(which is the literal meaning of T-8: 8/8 inch, as opposed to T-12 =
12/8 inch), 2,wattage (4-foot 32-watt, 3-foot
25-watt, and 2-foot 17 watt), and 3, their markings
("FO-32", "F32-SPX" "TL7xx", etc., depending on manufacturer). T-8's use a
different (but inexpensive) type of ballast, so you should
not use them interchangably with standard fluorescents. The
one trick with T-8's is that you may need to get the tubes and
ballasts from a commercial lighting supplier (check the phone book).
Tubes are available in 5000K and 6500K color balances, ideal planted
tanks, but they may need to be special ordered.
One word of warning, there are some standard fluorescent tubes that
are T-8 diameter, most notably 18" and some 36" tubes. These should
not be mistaken for the above bulbs, and should be used with normal
ballasts. When in doubt, make sure to check the wattage and
identification (3-foot 30 watt and 18-inch 15 watt bulbs are not
the new kind).
``What's MH? Is it better than fluorescent?''
Metal Halide (MH) lights are most commonly seen illuminating football fields,
but are also used in our hobby by reefkeepers and die-hard plant enthusiasts,
who demand very high light intensity.
The fixtures cost significantly more than fluorescent (over $200 per fixture).
The bulbs last longer and provide more efficient and brighter
illumination than fluorescents (typically 175-250 watts per bulb), but generate
an appropriately higher level of heat as well.
Some aquarists like the sun-like shadow effects
generated by MH bulbs.
``Can I use those cheap Halogen bulbs from the hardware store?''
Do not confuse MH with the tungsten halogen lights sold in hardware
stores as utility floods or living room fixtures; Halogen lights are
basically high-wattage incandescent lights, and generate an enormous
amount of heat and are very inefficient in their light output. Some
also find the spectrum too yellowish.
``How do I add another light to my tank?''
If you can fit a second tube in your
existing hood, many stores sell upgrade kits to add the second fixture.
Otherwise, you might be able to add a second hood to the tank,
or you can find a replacement two-bulb hood (mail-order places sell them).
Another option for 4-foot (130cm) long tanks is to buy a ``shoplight''
fixture and lay
it across the top over the glass. You can also build your own hood or canopy
and mount the shoplight or fixture inside. It's possible to omit the fixture
by purchasing special end caps and clips for the tubes. These are available,
with ballasts, from aquarium stores and are commonly used by marine aquarists.
``How long do I leave the light on each day?''
Plants want a definite daily light and dark cycle each day; 10-14
hours is fine; twelve hours is the duration on the equator, where many
tropical plants are found.
You should buy a timer ($5-10) to automatically turn the
lights on and off for you, since the plants (and fish) prefer a regular cycle
to an erratic one. If the plants need more light, you should not
extend the light period, as that will only help the algae. Rather, install
another fixture and increase the intensity of light.
Speaking of timers, many fluorescent fixtures don't self-start, i.e. you
have to hold in a button for a few seconds to turn it on. You can quickly
convert any fixture into a ``self-starting'' one with a few new components
from a hardware store or sold as a kit from mail-order houses. See the
later LIGHTING section for a diagram.
``How often do I change the bulb?''
Most fluorescent bulbs lose a major portion of their intensity after six months,
so they should be replaced every 6-12 months (T-8's can be kept
longer). If that seems expensive
to you and you can live with the reduced light level,
you can cheat and wait until the bulbs burn out after two years
(that is, according to TAG editor Neil Frank,
what ``many experienced plant enthusiasts'' do).
It is best to
stagger the replacement on multi-bulb tanks in order to avoid dramatic
``Won't increased light fill my tank with algae?''
If you are adding that second light to your tank for the first time,
you should be prepared for this. Increased light is welcomed by both
algae and plants, so the plants must out-compete the algae.
You can help tip the balance in the plants' favor
by maintaining a low fish population,
keeping algae eaters,
and frequent water changes (see the ALGAE SECTION
of the DISEASE FAQ).
``Is CO2 injection really necessary?''
CO2 injection is not required to grow plants. However,
most people who have used it feel that, aside from high-intensity lighting,
CO2 is the most important step to getting excellent growth.
In fact, as light intensity is increased, plants will require more nutrients,
including carbon which is derived from CO2.
In conjunction with carbonate buffers (see the
WATER CHEMISTRY section of
the BEGINNER FAQ), CO2 injection
will buffer your water to a neutral or low pH. Lower pH will help plants get
access to certain nutrients. Some also report CO2 injection keeps algae down.
``Isn't CO2 expensive?''
The startup cost can be a bit steep; expect to pay around $500 for a
fully-automated Dupla system, $350 for a manual injector. If you
do it yourself using
welding or bar supplies, you can
drop the price to $100-$200 for a tank, regulator, and needle valve.
After your initial investment, CO2 refills (try fire extinguisher
or beverage service outlets) are cheap: $5-10 a year for a 5 lb
If this is still too much, try the ultra-cheap Yeast
Method of brewing CO2 (see below).
``How much CO2 is normal?''
The optimum dissolved CO2 level in an aquarium is 15-20 ppm.
Some references say that levels above 25ppm poison your fish, but
general experience is that this doesn't happen.
The amount found in the water from atmospheric concentrations varies by
elevation and temperature, but is less than 1ppm.
``How does the compressed gas method work?''
A compressed gas cylinder supplies CO2 at a high pressure of 800-1200 PSI.
This is dropped to 5-20 PSI through a regulator, and reduced to
a few bubbles per second by a fine-control ``needle valve''.
This slow bubbling
must be dissolved in your aquarium's water, through either a
gas reactor (which lets water and gas mix in a chamber much like a trickle
filter), an inverted jar (which just lets the gas diffuse into the water
slowly), or by injecting the bubbles into the intake of a power or canister
filter (the impeller
``chops'' them up into smaller bubbles, many of which dissolve). The reactor
is the most efficient method, while the power filter injection is the easiest
It is important to have control over the rate of injection, as too much CO2
can kill your fish.
Expensive ``automatic'' systems use an electronic pH meter to regulate the
amount of CO2 in the water by shutting off the gas when the pH drops too low.
``Manual'' systems require you to start with very low injection and gradually
increase over several days, all the time
carefully monitoring pH drops and CO2 bubble rate in order to find
the correct needle valve setting.
Construction and operational details can be found in the later
``How does the yeast method work?''
CO2 is generated by fermentation of sugars in a bottle
(just like when brewing beer!) and then injected into the tank using
the same methods described above. The parts are very cheap
and easier to set up than the compressed tank. The main drawback is
that CO2 generation rate can be erratic, and will quit on
you if you do not change the solution (once every two weeks or so) or
get the mixture right. The CO2 level generated is lower
than that of compressed gas tanks, but is still enough to help plant
growth. Initially passed off as ``useless'' by much of the aquarium
literature, this technique has enjoyed a certain vogue in the last
few years as a good way to try CO2 without draining your wallet.
Here is one quick construction method: Tap the cap of a 2-liter
plastic soft drink bottle (the author uses drip-irrigation taps, which
can be obtained cheaply at local hardware stores; if you get leaks,
try sealing it with ``Amazing Goop'' or ``Shoe Goo'') so that an
airline tube can feed the gas into your tank. Half fill the bottle
with water, and add 1/2 tsp yeast and 1/2 cup (or more) sugar. The solution
will last about two weeks, after which you can throw it out and start
a new batch. Beware of water siphoning back from your tank... put a
check valve in-line with the airline tube.
``Can I just dump carbonated water into my tank?''
No! Plants need a slow continuous source of CO2. If you dump
carbonated water in, it will spike the pH (stressing your fish), and
the CO2 will just dissipate back into the air within a few hours.
``Does injecting CO2 reduce the oxygen content?''
No. The level of dissolved CO2 and oxygen are actually independent
of each other; high levels of both can exist at the same time.
Furthermore, if you have a set of healthy plants, they will be saturating
the water with oxygen on their own. The problem is that many of the
techniques used to increase oxygen content (airstones, trickle filters,
keeping the water moving at the surface) also cause CO2 to diffuse
out of the aquarium; i.e., if you turn off your airstone
in order to keep the CO2 in, you might also
reduce your oxygen content. The best solution is to keep the water
moving at the surface of the tank, but inject CO2 faster than it can escape,
giving you high levels of both CO2 and oxygen.
``Is fish food enough to fertilize my plants?''
Fish food usually provides enough of the three macronutrients,
nitrogen, phosphate, and potassium (N-P-K),
to keep your plants healthy. However,
the trace elements such as iron are not all supplied in a form that the plants
can use. Some trace elements may be in your tap water, so frequent water
changes will replenish them. This may provide enough for some plant growth,
but if you want the best growth you should consider adding a trace element
``Can I use normal plant fertilizer?''
Normal land plant fertilizer contains high amounts of N-P-K which is
already supplied by the fish food. Adding more will cause algae outbreaks
and possible fish stress. You may be able to find a trace-element-only
fertilizer at better garden shops, or even mix your own. Aquarium-specific
mixes by Dupla (available world-wide) and Dennerle (not available yet in the
U.S.) are expensive, but are proven to work very well.
Beware some other brands that supply N-P-K (check the label
for ingredients; some do not list their contents for this exact reason.)
Fertilizer tabs, or even 1/4 inch pieces of ``plant sticks''
(without sulfates) have been successfully used if placed deeply in the
substrate and used sparingly.
``How do I know if I need fertilizer?''
Lack of fertilizer shows up in your plants, as sickly transparent
or yellow leaves, as holes in the leaves, and as reduction in plant
growth. Old leaves die off
more quickly than they are supposed to, and the new leaves are small
and stunted. Another symptom is the plants grow very well for a month or
so after you buy them, but then stop as their internal supply of trace
elements and macro nutrients run out.
You also need to add fertilizer if you have high levels
of CO2 and lighting, but no plant growth.
``How do I know which nutrient is limiting plant growth?''
This is always difficult to answer without actually trying
it yourself. If you have slow growth and it picks up shortly after you
change your water, then your water is probably
supplying some trace elements which
get depleted later; consider adding a trace element mix or changing your
water more often. If you have
slow growth, but it picks up after adding trace element mix, problem solved!
If you have slow growth but it picks up after feeding your fish a little
bit more, problem solved! But watch out that you don't increase things too
drastically, or you'll get algae blooms.
``How much is too much?''
If you like keeping zillions of test kits, then you can check some trace
levels with them (Dupla recommends an iron level of 0.1ppm). Ammonia and
nitrate test kits will tell you if you are overfeeding.
you need to watch your tank. Too much fertilizer and fish food may show
up as excessive algae growth.
``What's PMDD? How do I make it?''
PMDD (or Poor Man's Dosing Drops) is a do-it-yourself recipe, put
together by Kevin Conlin and Paul Sears as part of their experiments
to control algae. Much discussion an experimentation with the recipe
is occuring on the Aquatic
Plants E-mail List, so you are likely to get the most current info
updates are kept on the WWW at THE KRIB. Future updates of this
FAQ may include sources and recipes when things settle. :)
``What should I put in my substrate?''
Gravel or sand is a good start!
Size is an issue; with small grains
the roots might not be able to get a good hold and the sand tends to
while larger gravel has a tendency to collect
pockets of rotting detritus. Most believe the ideal size is
2-3mm (#8) gravel, while
a few others like 1-2mm coarse sand (though it may be harder to find).
Malaysian trumpet snails
(see the ALGAE SECTION of the DISEASE FAQ)
will burrow into the
substrate and keep it aerated.
The bottom 1/3 of the gravel can be supplemented
with a fertilizer, of which popular choices are peat (softens water),
laterite (a clay containing iron, usually used with undergravel heating
systems), and soil.
One word of warning: if you use
an undergravel filter, it may suck your fertilizer back into the tank instead
of keeping it with the bottom of the gravel. Dupla makes special
laterite balls which can be used in an UGF (though expensive).
``How deep a substrate?''
In general, it's good to match the substrate with the types of plant (or
types of roots). For instance big Amazon Sword plants like deep gravel of
4 inches (10cm),
but Lilaeopsis grass can do fine with an inch or less. This can be
helped by terracing the back of your tank to be deeper and planting
your deep-rooted plants there. You also can't go wrong with a uniform 3 inches
(7cm) of gravel all-around.
``Can you grow plants with an undergravel filter (UGF)?''
Oh my yes! Make sure you have enough gravel for the plants to be happily
rooted. It should also work best with a very slow flow rate.
Pluses of UGF may be an increased circulation to the roots. However,
you will probably get roots growing in the plates, it will be
harder to vacuum everything, and will be a major pain to pull and replant.
Many feel so strongly that you shouldn't grow plants with an UGF
that it has become a bit of a religious issue on Usenet. However, this
does not mean it is not possible... like most religious issues, it is something
for which you must make your own decision. :)
``What temperature do I keep a planted tank?''
This varies from plant-to-plant, but you can keep most aquatic plants
from 72-80F (22-27C). For warm-water discus tanks, check a plant book for
species that thrive in these special conditions.
The exact benefits of substrate heating have not been proven yet, but
it is believed they provide long-term stability to a tank.
If you are a beginner, it's hardly worth messing with before mastering
the basics (fertilization, lighting, etc). If, though, you
are a gadget freak or love to spend money, you may get a sense of pride
from installing a cable heating system.
(Some believe that a very slow UGF can provide
the same benefits.)
This list is by no means exhaustive! Please feel free to suggest more
long-term problems that can be addressed here.
``The leaves turned yellow and fell off.''
``The leaves got holes & fell off''
Might be a trace-element deficiency, or in the latter case, fish and
plants eating them.
``It grew for a while & then died/still grows, but slower.''
This is by far the most common problem beginners experience, and has
several different causes.
- Plants can
store some nutrients and trace elements, using them later. When they come
from the greenhouse, they are fully stocked. But after a month or more,
if you do not supply them with a balance of nutrients they take what's
missing from their stock. When the stock's gone, the plant dies.
- Most potted
plants are grown emersed (hydroponically) in greenhouses, and are
used to growing in very high light (i.e. filtered sunlight) and with high
levels of nutrients, and must acclimate to aquarium conditions. First,
they'll lose the old leaves which were growing out of the water and produce
new leaves that have a different shape and firmness. Secondly, as they
acclimate to the lower light and nutrient levels their growth rate will
temporarily slow down.
While potted plants ship well, this may not be true
for non-potted plants. They may have been stressed by passing through
many hands from grower or collector to wholesaler to retailer, so they may
not be in optimum condition when you acquire them. The non-potted plants
were most likely grown underwater, but also outdoors under filtered
sunlight, so they also must acclimate to the aquarium conditions.
- The plant might not be a true aquatic plant. Many stores pass off
land plants as aquatics (see our
These plants can manage
to stay alive for a month or more, but eventually succumb.
- Some plants go into hibernation.
Aponogeton bulbs will
lose all their leaves, at which point they should be removed from the tank
and kept in cold water for a few months. Then they can be replanted and will
send out new leaves.
will ``melt'' all their leaves on a change in water
chemistry. Don't despair, eventually they will send out new leaves.
``My ... grows great but everything else dies''
Some plants are hardier than others, and will grow in lower light,
CO2, or worse water conditions than others. However, some plants
will actually out-compete others for the available nutrients, and
some plants will not do well in the presence of other species; try moving
the other plants into a different tank if you can.
``My ... is covered with algae!''
Please read the
ALGAE SECTION of the DISEASE FAQ
for details on specific algaes and remedies.
But to summarize,
you can keep algae-eating fish to munch on it,
starve it for nutrients by adding floating or fast-growing plants that
consume nutrients faster than the algae,
harvest some plants and remove
dying leaves often to take nutrients out of the tank,
reduce feeding (or increase water changes if you must overfeed),
reduce the number of light hours per day,
use root fertilization instead of liquid leaf fertilization,
or physically remove it from the tank. There are also antibiotics for
blue-green algae and other algicides,
but the latter can kill your plants as well; use with caution!