Algae in the Planted Aquarium
Algae is probably every planted aquarist’s worst enemy. Almost everyone will have experienced it at some point to some degree, whether it is minor hair algae through to a Cyanobacteria (Blue Green Algae – BGA) infestation.
The good news is that it is possible to run an algae free tank, long-term without resorting to all sorts of complex methods. To do so one needs to understand some basic principles.
Please note – I make a few assumptions regarding alleochemicals in this article, they may not be scientifically accurate but they illustrate the points I am attempting to communicate effectively. Forgive me anyone who disagrees with anything I write, please let me know if you have any concerns.
The principles discussed are aimed at tanks that are well-planted i.e. more than just a couple plants, ideally at least half the substrate should be covered. A lot of the principles are not entirely relevant to Low-Tech tanks either, as pioneered by Diana Walstad. These rely on different principles to keep algae away (although the alleopathy is still relevant). I apologise to anyone who runs a low-tech aquarium that doesn’t find this article helpful.
Much of the content in this article is repeated from the lighting, CO2 and EI articles. I do not see this a problem though as it bodes well to re-iterate some important points.
Algae versus Plants
In a planted tank there is a constant battle between lower plants (algae) and higher plants (normal plants we want to grow).
Basically if plants grow well then algae doesn’t, and vice versa. Algae’s worst nightmare is a tank full of healthy, growing plants – the better the growth the less likely algae has a chance. This is why fast-growing plants (generally stem and floating) are ideal algae-busters.
The reasons for this are fairly complex but put simply plants produce alleochemicals when growing. These chemicals act like a form of chemical warfare known as alleopathy – it is a principle found throughout nature in plant forms and includes even marine corals. It is this alleopathy that fights off algae.
Growing Plants and Balancing Parameters
If you have read the other pinned articles about lighting, CO2 and EI then you should have a good idea how to grow plants successfully. It is worth reading these articles prior to this as a lot of the subject matter relies on some basic knowledge on these subjects.
It is vitally important to achieve the correct balance of lighting, CO2 and nutrients. I won’t go into detail as the info you need is in those articles but to reiterate; you need CO2 with over 2 WPG light; CO2 needs to be stable at approx. 30ppm and if you have these light levels and CO2 you will need to dose regularly with macro and micronutrients. Remember that plants need access to all nutrients (including nitrates and phosphate despite popular opinion – read the EI article!) If one nutrient goes deficient then the plants slow/stop growing giving algae the upper hand. If all these parameters are in harmony and there is a largish planting density (bio-mass) then algae won’t stand a chance.
With lower lighting and no CO2 injection you may not need to fertilise with macro or micronutrients at all – regular water changes and fish food/waste may provide adequate nutrients. It is still important to plant heavily though to stand the best chance of beating algae.
Algae and Lighting
Lighting is obviously necessary for plant growth. Unfortunately algae also love light. It is therefore very important that we provide the correct type and quantity of light to benefit the plants as much as possible – therefore providing us with the best chance of beating algae.
Avoid lighting with a high blue content i.e. tubes sold as suitable freshwater and marine. These normally have a high colour temp. i.e. >8500K. There are exceptions to this though that I will discuss.
Low Light versus High Light
Low Light
If you have less than 2 WPG then you may not want to inject CO2. This lower light level combined with no added CO2 will result in slower plant growth. Slower growth leads to less alleochemicals and therefore more risk of algae.
It is therefore very important that we choose the best tube(s) possible for our tank. As discussed tubes that have a lower blue content are ideal, one of the best examples of such a tube is the Dennerle Special-Plant T8. This is 3000K and gives a warm, yellow/orange light. It has virtually no blue content and so does not promote algae. Combining this tube with a higher K tube will produce a very nice colour balance in my experience. Full-spectrum, daylight tubes are regarded as the best plant growth tubes. Read my Lighting article for more detail.
Medium to High Light
With over 2 WPG, CO2 must be added, as you will hopefully know already. This much light and CO2 will result in faster growth leading to more alleochemicals and thus less algae.
Tube choice, in terms of colour temp. etc. therefore becomes less important - instead sheer quantity of light is the priority.
You could therefore use much higher K rating tubes with no problems if for example; you have lots of light (i.e. >3WPG), stable (i.e. 30ppm) CO2, plenty of nutrients (i.e. EI) and a high plant bio-mass (i.e. 50% substrate covered in medium to fast growers).
Many US planted hobbyists use much higher K rated tubes than normally recommended. I have often seen beautiful tanks lit with 9532K, 10000K and even 14000K with no algae issues whatsoever. This confused me a great deal at first until I made the connection between plant growth rate and algae busting. The plants are able to utilise the high blue content to their advantage due to the high light quantity, CO2 and nutrient levels. I have even heard of actinic tubes being beneficial. I believe the higher K tubes (9532K, 10000K) are popular due to their pure white light and good colour reproduction. As long as the plants grow well then algae does not.
The beauty of this concept is that you can choose pretty much any colour temp. you wish according to taste, availability and budget. Personally I still like to use dedicated “plant growth” tubes. For your interest I use a combination of Dennerle (3000K) and Arcadia (7500K) – unfortunately these are only available in Europe to my knowledge.
Getting it Right From the Start
The easiest way to deal with any algae problem is by preventing it. We already know that we need to have the correct lighting, stable CO2 and nutrient balance. But, perhaps the most important aspect to maintaining an algae free tank to plant it heavily enough.
This is particularly important when setting up your tank from the start or performing a strip down/re-aquascaping.
A “sterile” tank i.e. one that is newly set-up or has had a major overhaul (substrate change, re-planting, heavily medicated etc.) will be particularly susceptible to algae as it lacks the necessary biological/chemical balance required to fend off any algae. This is why it is essential to plant heavily with fast growing plants as these quickly establish this necessary biochemical equilibrium. Once the tank has established, say after 3 months or so, then you can swap your fast growers for any slower growing, more demanding plants.
If you are starting out then I suggest the following steps to help achieve a long-term successful, algae free tank.
1. Buy all the right equipment – upgrading as you progress is fine as long as you get the basics right from the start.
You need (I haven’t included the obvious stuff i.e. tank) –
i) Good biological filtration, externals are the best option, avoid excessive surface agitation is this drives off CO2 .
ii) Suitable lighting
iii) CO2 (if required)
iv) Substrate (nutrient-rich preferably)
v) Fertilisers (if required)
vi) Test kits – ammonia, nitrite, nitrate, phosphate, pH and KH (if you inject CO2)
2. Get your CO2 stable (aim for 30ppm) before commencing lighting.
3. If using dry ferts (EI) then sort out your solutions/planned regime.
4. Plant heavily from the start. Cover at least 50% of the substrate with fast-growers.
Examples of Algae-Busting Plants –
Hygrophila species
Ludwigia species
Rotala species
Egeria species
Brazilian Water Ivy
Small Ambulia
Mexican Oak Leaf
Water Sprite
Hornwort
Floating plants (careful they don’t block too much light)
5. Use a plug-in timer to control your photoperiod. I run a siesta that in my experience helps to further prevent algae. 5 hours on, 2 off, 5 on is ideal. I have tried many combinations of photoperiods from 12 hours on down to 4 on, 4 off, 4 on and find that 5-2-5 gives an ideal balance of plant growth and algae prevention. Many aquarists do not run a siesta and experience no algae problems; this is fine and is really a matter of personal choice.
I do not fully understand the science behind the siesta helping; all I know is that is works well in my tank.
6. Keep your tank well maintained –
Change around 25% water per week minimum; EI users normally change 50% per week. Do not over clean your biological filtration.
Keep the water well fertilised if necessary – particularly if you have >2 WPG and CO2. Test water regularly for CO2 (if used), NO3 and PO4 levels (more on this later).
Prune your plants regularly as required – plant cuttings from stem plants to increase plant bio-mass further helping to win the battle against algae.
Try to keep the substrate fairly clean, this becomes harder as you become more planted but it is possible to siphon detritus from the substrate surface. Thankfully a heavily planted tank uses up a lot of the detritus etc. as a food source.
Stock with plenty of plant friendly algae eating fish/inverts. For smaller tanks Otos and Amano shrimp are ideal. Siamese Algae Eaters (Crossosichlius siamensis) and Bristlenose plecs are ideal for larger tanks (as well as Otos and shrimp).
Malaysian Trumpet Snails are great planted tank maintainers in my experience. They do not eat plants but will eat algae. They live in the substrate mostly during the day, eating waste food etc. and turn over the substrate helping to prevent too many anaerobic dead spots that can lead to problems such as BGA and Hydrogen sulphide.
Nitrates, Phosphates, Ammonia and Algae
In a well-planted tank nitrates (NO3) and phosphates (PO4) are NOT the enemy as previously assumed by most schools of thought.
It is ammonia/ammonium (NH3/NH4) that is the biggest algae trigger; this is why it is essential to have efficient biological filtration and why you must not overstock a planted tank with fish. Simply adding more fish or over feeding to increase nitrates is not a good idea for this reason, the slightest ammonia spike (remember that ammonia is never actually zero, there is always some in the water until it has been bio-filtered) may be enough to cause an algae bloom.
It holds true that too much NO3 and PO4 may results in algae growth but these levels are much higher than previously thought, particularly in a heavily planted tank with good growth.
To re-iterate, if NO3 and PO4 are deficient then plant growth slows or stops therefore leading to algae gaining the upper hand. This is why it is important to dose these nutrients in high growth set-ups. If you have a low light tank with no CO2 then your fish, fish food/waste, and tap water may provide adequate levels.
Aim for -
NH3/NH4 - undetectable
NO3 - 5 to 30ppm
PO4 – 0.1 to 2ppm
With lower light and no CO2 tanks then aim for the lower figure.
Higher light and CO2 then aim for the higher figure.
These figures assume you have a healthy (in terms of quantity and growth) plant bio-mass.
Follow these above guidelines and you should never have algae issues.
But I already have an algae problem – how do I get rid of it?
So you should know by now how to prevent algae but you need to get rid of an existing problem.
My advice would be to –
1. Set up your tank according to the above guidelines; invest in better equipment if necessary i.e. lighting, CO2 or filtration. If you are using sub-standard equipment then you will be constantly fighting a losing battle.
2. Ensure your lighting/nutrient balance is correct. Test NO3 and PO4 levels – adjust accordingly via dosing ferts or diluting with water changes. If PO4 is too high and your tap water has a high content then consider a phosphate removal resin i.e. RowaPhos. Excessive PO4 or NO3 should never be a problem in a high growth set-up. Ensure micronutrients are dosed correctly.
3. If injecting CO2 ensure it is STABLE at approx. 30ppm.
4. Remove any algae infected leaves. If the plant has a major infestation then discard the whole plant. Sometimes a bleach dip may work; I have no experience of this though so I suggest researching this method further.
5. Plant over 50% of substrate with algae-busting plants (see list above) to create a healthy bio-mass.
6. Use a siesta in your photoperiod. Do not light for more than 10 hours. Ensure that your tank receives minimal natural light. Direct sunlight is a massive algae trigger in particular.
7. Reducing lighting intensity and/or photoperiod can work for some cases. However this can also have a negative on plant growth thus increasing algae. Planting more heavily with fast-growers and keeping the lighting the same will probably be the best option.
8. If you buy new lighting then change one bulb (if you have multiple tubes) at a time as this prevents photo shock that can harm the plants. Plants can take some time to adjust to new light intensity and spectrums. Even if you buy the same brand of tube the intensity and spectrum will be different as it changes over time. Personally I like to replace my T8 fluorescents every 12 months. I have 4 tubes in my tank and replace each approx 3 months apart. This way the new lighting is staggered preventing photo shock and my pocket isn’t hit so hard for cash (4 tubes at once is expensive!)
9. Avoid algaecides. These may kill off your algae but if you don’t change your set-up accordingly then it will return with a vengeance. It is always better to remedy the cause rather than the symptom.
Cyanobacteria (BGA)
Strictly speaking this is not a species of algae but a form of bacteria. It does, however, act in a similar fashion to algae and can be prevented using similar principles.
I am no expert on BGA (or algae for that matter) but I can share my experiences with it in the hope that it may help you.
Also known as Slime Algae, due to its physical nature, it covers the substrate and plants with a blue/green slime like substance. Untreated this will spread very quickly smothering everything, substrate, plants and décor. It out competes the plants for nitrogen and prevents photosynthesis due to it blocking the plants from the light. It is also toxic to fish and nothing will eat it. In short it is nasty stuff – it even has an unpleasant smell. This is one method of confirming it is BGA.
I understand it originates in the substrate, this is certainly true in the couple of cases I have had. I am unsure as to what the true cause of its manifestation but I think stagnant water helps it and the anaerobic bacteria associated with it. Low nitrates and natural light are often associated with its spread too.
Prevention
As with “normal” algae, prevention is better than cure. These steps should help.
1. Set-up your tank according to the above principles – in particular keep nitrates above 10ppm.
2. Avoid as much natural light as possible.
3. Try to keep the substrate from going too anaerobic. Some anaerobic areas are necessary and are found in nature. Poke the substrate occasionally, particularly if you have sand. Substrate heating can also be helpful in my experience. Hopefully with lots of root growth the oxygen produced will prevent too much anaerobic build-up.
4. If you see a slight BGA build-up between the substrate and glass (this is normally the first sign) then disrupt is by using a credit card. Slide it between the front glass and substrate. This should stop it from spreading to the substrate surface.
Treatment
There are two main methods to treating BGA. The first is a blackout. Cover the tank completely; do not let any light in at all. Wait for 3 days, no peeking or feeding the fish, then uncover, hopefully the BGA will have disappeared. I have not personally used this method but I am assured it works (except for Houndour’s case – sorry Sam).
The second is by using antibiotics. Remember that BGA is bacteria. Ethyromycine (trade name - Maracyn) is commonly used to rid BGA. It is also highly effective and is apparently fish and plant safe. The whole tank is normally treated via mixing the drug with the tank water. Dosage - 200mg per 10 US Gallon every day for five consecutive days.
I have had good results with Maracyn using another method. I recently witnessed a little BGA build-up between my substrate and front glass. I split a 400mg Maracyn tablet in half, then one half I broke into 8 small pieces. I placed each piece in the infected areas using tweezers. A couple of days later the BGA had completely disappeared. Now I slide a credit card between the glass and substrate every week just to ensure it doesn’t reappear. So far so good (8 weeks on) and I still have 99 ½ tablets left!
In Summary
You will not experience any algae issues if you have a tank full of healthy growing plants.
It is creating the ideal conditions to grow these plants that is the key. If you have the right balance of light, nutrients and plant bio-mass then your tank will be virtually algae free, with any small amount of algae growth being taken care of by your algae eating fish.
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