The first step to sorting out algae is figuring out what type of algae you have in your aquarium. The reason being is that different types of algae are dealt with in different ways and you also need to sort out how to prevent it from reoccurring. Disclaimer: Below is information that I have worked out over the past few years. It is all my personal experience therefore this is all anecdotal. Anyway let’s get to it.
WHY am I getting algae in my tank??!! It’s so frustrating!!! Once you understand the situation better and really think about how it’s functioning you will be more equipped to troubleshoot. Think about this, You’re trying to emulate nature in a glass box. The aquarium light is the sun, the filter is the water current + house for the bacteria to reside in, the water change you do is when it rains, the filter and substrate are also home to the beneficial microscopic organisms you’re wanting to be your house cleaners (since they are in charge of processing the waste into nitrogen which is the primary source of plant food and keep the ammonia at bay in order to prevent algae spores from germinating), and the heater is there to emulate the tropics in order to achieve faster plant growth (since plants grow slower in cooler temps). If we don’t get these things correct or they are not working harmoniously with one another you can get algae and sometimes fish illness. Also remember that in nature, aquatic plants may not necessarily grow in direct sunlight, they often grow in semi-shaded areas where bigger trees overhang or in water that is deep enough to diffuse the suns light. It is for this reason that aquarium lights are almost never as strong as the sun’s rays. It is also not wise to have direct sunlight shining on your tank, especially if the tank has algae.
The ideal situation is when the tank is “balanced”. The word “balance” is used flippantly, but all it means is that this man made environment has become a fully fledged eco-system that is self-maintaining yet still reliant on your input and in some cases has actually become accustomed to your input and its current state. Another way to put it is your eco-system is naturally occurring yet working in perfect equilibrium with what you are artificially providing it (light, water movement, fertiliser, inhabitants, heat, fish food). To be specific, a balanced tank would mean that the plants have everything they need to flourish – correct Light levels, food, carbon, and the beneficial bacteria and fungi that are all perfectly populated in their ideal ratios consequently processing the amount of fish and plant waste that NEEDS to be processed at any given time as opposed to too much waste versus not enough “house cleaners” causing “ammonia hot spots” in the tank that wouldn’t necessarily register on an aquarium test kit. Essentially the beneficial microbes are your main water purification system that are creating a clean and ideal habitat for the plants to live in as well as contributing to their number one food source – nitrogen. Our goal is to have all the variables mentioned above working harmoniously in order to achieve “The Balance”. So… Is your eco-system a functioning unit? And if not, how can you make it better? It is important to note that new tanks are never functioning eco-systems as they can take weeks to become mature, therefore, be patient, as “new tank syndrome” can be disheartening since new tanks go through a plethora of unbalanced fazes. White water bacteria bloom, green water, diatoms, and green dust algae to name a few. Aside from the nasty fazes a new tank can go through and once those things pass, the above is a lot to think about for a beginner and more often than not the plants “just grow” without you even knowing what is going on behind the scenes.
Green Dust Algae (GDA)- Scraps off easily, primarily targets the glass but also targets plant leaves, it’s green of course and barely has a smell to it therefore do not confuse it with cyanobacteria, I have found that this algae occurs in new tanks especially or when the “Balance” gets jolted via rapid “change” in an established tank. Change might be, the filter was left off for a couple of days and the nitrogen cycle was disrupted, or you changed your fertiliser routine and your plants went into momentary shock, or you trimmed half your tanks plants away and left it bare causing a sudden burst of light with hardly any plants that are even used to that amount of light causing a nitrogen boom from lack of nitrogen uptake via happy plants that used to be there! Or, you dosed your tank with hydrogen peroxide to kill BGA and got an ammonia spike, or you accidentally used far too much flourish excel (which I believe sterilises the tank to a certain degree killing off beneficial microbes/house cleaners. Thus your eco-system is no longer a harmonious functioning unit. The consequence is green dust algae. I have come to realise through copious amounts of googling that the exact and precise cause of this algae is not quite known but there is speculation from various sources that green dust algae is caused by too much nitrate to phosphate ratio. Whether this is true is another story. I have not found any evidence of this personally but a sudden influx in nitrogen would be a sure method of inducing it. Others say that if you keep your phosphate to nitrate levels sufficient it should inhibit its growth. I have also noticed that it is far more prevalent in Co2 injected aquariums (high tech) over non-Co2 injected aquariums (low tech).
To Fix let the algae sit on the aquarium glass for as long as it takes for it to start to flake off a bit and go patchy. This can take anywhere from 2-4 weeks. Once you feel confident the algae has lived out its life cycle and the tank has found its balance again, scrub it off followed by a decent sized 50% or more water change. It shouldn’t return, but if it does, do the process again. Handy Tip: Put some floating plants like ludwigia Repens and Hydrocotyle Leucocephala in the tank in order to diffuse a bit of light, and whatever you do keep natural sunlight away from your tank!! When it comes time to remove the floating plants, remove them gradually as opposed to blasting the tank with sudden bouts of light. In the pic below you may notice it is starting to go patchy on the right hand side thus It is nearing the end of its life cycle, as a fresh bout of GDA would be thinner and more spread out. Pic of Greendust Algae taken from Pinterest 
Blue Green Algae AKA Cyanobacteria (BGA) – Bluish green colour in freshwater tanks, Rubs off easily, has a distinctive smell like no other. So potent that if you touch it your hands they will smell like it for 10 minutes afterwards. It is actually an anaerobic bacteria and not a true algae. I have found that this algae only occurs in tanks with high light. Or areas where light is concentrated. I can’t say I’ve ever had to deal with it in my medium to low light tanks. Another common cause of it in high light tanks is when you forget to dose your fertiliser and leave the tank deprived of nitrogen for a few days or more, particularly in Co2 injected tanks since they are more vulnerable in the sense that the consequences of mistakes are accelerated since everything (including algae) is able to grow at a much faster rate than without Co2. The most common area for BGA to form is the area where the substrate meets the glass at the bottom of the tank. That is where light is able to hit and there is also very little oxygen. Once it gets to the top of the substrate it begins to crawl across the substrate infecting other areas of the tank. BGA loves high light and low oxygen environments making this area a prime spot. Easy fix is to put black tape around that area on the outside of the glass.
In order to eradicate BGA there are a few methods. For heavy infestations of it, remove most of it by syphoning it up in a water change, then dose the tank with 3% Hydrogen Peroxide at 1ml per gallon (3.8l). Don’t spot spray because if fish swim past concentrated areas of it can damage their skin or eyes. You can dose twice in one week followed by a large water change to remove any small amounts of ammonia. Remember that this will upset the balance by causing a 0.5 ammonia spike at most. Tip: Hydrogen peroxide 3% is expensive for what you get, consider buying 35% off trademe and dosing 11 times less. A less invasive method is to spot spray white vinegar with a syringe at 5mls per 50L daily for a week on the badly affected areas. This can be used as an extra kick after the H202 dose or try it initially and see if you get any results. You will need to check your PH daily though since vinegar will lower your PH. Vinegar is not harmful to fish since it is a naturally fermented product but it is acidic and antibacterial so it can upset your beneficials to a small degree, but nothing serious. You could go and buy some Boyd Chemiclean which I believe is another type of oxidiser however I’m not sure which one as they don’t list their ingredients on the box. I’ve heard it works well but it’s quite expensive. Even though BGA attaches to surfaces, a UV steriliser does add some assistance to destroying its presence. The last method of killing cyano is by using potassium permanganate (PP). It’s available at farmlands, trademe, and oderings website, as well as many garden centres. The PP method is easier if you don’t have fish, however, some people use it in tanks with fish in small doses. You put a pinch of PP into a cup and add some water till it’s hot pink. Get a syringe and spot spray the areas where the cyano is, just be careful you don’t go crazy with it and turn your whole tank pink as it is harsh on beneficial bacteria. The one good thing with PP is it turns orange once it has done its job so there is no need to do a water change straight away as it is biodegradable. Hydrogen peroxide, vinegar and potassium permangante are all biodegradable which is a calming thought considering the harsh chemicals people have been known to dose their tanks with when using algaecides made for aquariums. Aside from killing off the BGA, the main thing you want to do is to prevent it from re-occurring thus make an environment that it hates. Also shield the exposed areas of substrate in your tank with plants. Add some floating plants even. A tank full of thriving plants is not an environment where cyano will thrive as thriving plants produce oxygen and oxygen is a known enemy to cyanobacteria. I’ve read that if you ensure your nitrogen levels don’t bottom out it will deter BGA from showing up or slow it down significantly. This is commonly spoke of on international plant forums. Pic of Cyanobacteria taken from FishLab.com
Staghorn Algae – looks like long blueish-greyish algae (not to be confused with black beard algae) I’ve found this occurs when Co2 levels get too low in a Co2 injected aquarium. Can also come about if you have far too much organic matter decomposing.
The fix – dose the tank with 3% hydrogen peroxide at 1 ml per gallon (3.8l). For a cost effective solution purchase 35% H202 off trademe and dose 11 time less. Once the algae has been killed, dose flourish excel daily according to bottle directions as a preventative or if you are running Co2 you need to increase your mg/L/ppm’s to around 30 or more. (How much Co2 to add is light and KH dependant, but a general rule of thumb is a minimum of 30ppm) Pic of Staghorn taken from FishLab.com
Black Beard Algae (BBA) – A type of hair algae that is short and greyish black in colour. This happens when you have too much organics decomposing in the aquarium. It also thrives in an acidic PH although don’t go raising your PH as that is not good for plant growth. It targets driftwood especially, anubias roots and slow growing plants. It also targets the older leaves of plants since the plant is no longer spending energy on warding off algae on its older growth.
To Prevent is to not overfeed your fish and syphon up any decaying plant material or uneaten food before it has a chance to decompose. Overstocked tanks are more difficult to manage due to having a high bio-load.
To fix you need to remove the plant leaves that are riddled with it and then double dose and spot spray the remaining affected areas with Seachem Flourish Excel. Don’t doubt dose the initial dose of flourish excel. You can only double dose the “Maintenance Dose” (bottle has two dosing types of dosing instructions). You will notice it turning pink once it dies. You can also dose flourish excel according to bottle directions as a preventative if your tank is prone to this type of algae. Pic of BBA taken from aquasabi.com
Green Spot Algae (GSA) – Looks like little green dots that target the glass and leaves of plants. Difficult to manually remove unlike green dust algae which is easy to rub off. This algae is common in aquariums where there are no fertilisers dosed. This is because fertilisers normally contain phosphate and green spot algae does not grow when phosphate levels are sufficient. I can almost guarantee that you will not experience green spot algae if you keep your phosphate levels at a sufficient level and do not let them bottom out. Sufficient being 1-2ppm.
To fix this algae all you need to do is raise your phosphate levels. Easy!!! Pic taken from FishLab.com
Spirogyra Algae – Looks like long green hair that can often appear tangled. This type of algae is nasty because it is difficult to eradicate. It comes in through other plants or if you induce it via heaps of natural sunlight shining on the tank combined with low Co2 levels.
To fix and prevent: If I see this algae on any plant that I receive I will dip it in a concentrated water and API algaefix solution (about 15 mls per 5 litres) for 24 hours before introducing it to my aquarium. The reason being is that API algaefix is the only algaecide that I know of that is capable of killing this specific type of algae. Unfortunately API algaecide is extremely toxic to fish and will either kill them or have serious effects on their health long term. If you decide to dose the water column with API algaecide it is best to remove your fish for the entire treatment duration, dose API Algaefix according to the bottle directions for 1 week, do a huge water change, then put your fish back. This SHOULD kill it completely so it does not return. 1.5 weeks would be the safest option however, particular tif you go through all the effort of removing your fish. API claim it is fish safe but it definitely is not and if you look up reviews on amazon.com you will quickly see. Straight 3% h202 is capable of destroying it in a 5 min plant dip however this is also very harsh on plants. If you do not destroy this algae in your aquarium it will forever plague you. No amount of flourish excel or h202 dosed into the aquarium will destroy it. Plant dips are another story but as I said before, they are harsh on plants. Pic taken from Plantedtanksource.com
Cladaphora Algae – Also known as Blanket weed. It’s green and doesn’t grow very tall, can actually look attractive to some degree. It has a rough texture in comparison to other types of hair algae. The cause of it I’m not entirely sure of since it’s not something I’ve had to deal with. Speculation and research online says it enjoys the same conditions as plants however it is capable of thriving in less than adequate Co2 levels. 5 years ago I got this algae on a piece of driftwood that was sitting near the air bubbler, it didn’t spread to other plants in the tank thus not making a nuisance of itself. I haven’t seen it since. Likely the cause was due to the air bubbles driving away Co2 from that area. This was not in a co2 injected tank so my available carbon levels were not high. It’s important to note that Co2 is still present in small amounts in non-co2 injected tanks so whatever Co2 that was present was being driven away from that specific area. Regardless of my experience with this type of algae, I’m sure it can be a proven pest in its ideal situations.
The fix would be to spot spray with flourish excel and in a Co2 injected aquarium you’d need to raise your Co2 ppm’s. Daily dosing of excel would be used to prevent it from re-occurring in cladaphora prone aquariums. Don’t keep your driftwood or plants near an air stone/air bubbles. This rule applies always regardless of whether you’ve seen cladaphora or not as plants near air bubbles barely thrive. Pic taken from Aquatic Plant Central
Diatoms – looks like brown dust on plants and glass. Rubs off easily. Can also appear alongside brown Rhizoclonium algae. Primarily happens only in new tanks due to excess silicates and ammonia leaching from the substrate. I have experienced this myself multiple times when using daltons aquatic mix thus I am never concerned when it shows up in a newly substrated tank as I know it will pass in time. You may avoid this “faze” when using an inert substrate that does not contain nutrients of any kind. The only OTHER time I experienced this type of algae was when my light spectrum was too yellow as opposed to the ideal “cool white” which I now solemnly use. I actually put a warm white lamp over one end of my 120cm long tank when my light hood broke and within a couple of days that end of the tank was riddled with brown slime (rhizoclonium) and brown dust (diatoms) on the leaves. The other end I had a white lamp and no algae or diatoms grew. To me this was proof that warm white light is never a good spectrum for growing plants under water.
To fix, ensure T5 and T8 lights are replaced according to manufacture instructions (normally once every 6 months to a year) and don’t purchase warm coloured LED’s or fluros for your tank. Red and Warm White chips are of course okay inside LED lights, as long as they are balanced out with sufficient amounts of blue and white light. In new tanks you just need to “ride it out”. It can take anywhere between a few weeks to few months at the most to disappear depending on the type of substrate you’ve used. Large water changes to hurry the process up. Otocinclus eat this algae. Pic taken from Reddit
Green Water – The water is now green and you can barely see into your tank. This type of algae only usually occur in newly set up aquariums and is caused from excess ammonia. A tank under 3-6 months old is susceptible as it has not yet matured into its “Functioning Eco-systemic State”. In short, the beneficial bacteria responsible for converting ammonia into nitrate are not at adequate populations. Green water can occur in mature aquariums but this would be caused from a sudden spike in ammonia. An example would be when bio-load (waste/decaying organics) increases to levels that the biological filtration (beneficial bacteria) can not keep up. Or an environment that is anaerobic therefore consistently in this state of havoc. This continuous state of anaerobic havoc could be the result of having no water movement whatsoever or the use of a toxic substrate that is uninhabitable for beneficial microbes to reside.
To fix, you can invest in a UV filter (you won’t need this long term) or you do a 3 to 4 day blackout followed by a very large water change. The blackout must not let any light into the tank so you’d need a thick black sheet or something that keeps the tank completely dark. These are the only two methods that I know work. Big water changes without the black out will not work at all. API make a product called Api Microbial Algae Clean (not to be confused with API algaecide which is a toxic substance) which contains a specific type of bacteria known as Bacillus licheniformis that can apparently control or prevent green water. It is a pond product however it would be safe for an aquarium since it is a biological product containing beneficial live bacteria. Pic taken from FishLab.com
Rhizoclonium – Looks like walls of very fine hair almost appearing like an upright wall of brown slime. It can also be green in appearance or a faded brownish green and appear at the same time as diatoms. I had this appear in a newly set up tank around about the same time as the diatoms showed up.
To fix: I dosed flourish excel daily according to bottle directions and eventually got it under control over the course of a few months. I believe this algae, to a greater degree, is present in newly set up aquariums and will eventually go away on its own assuming proper care and maintenance are given. Pic taken from Aquaticsforevers
White Cloud Bacteria Bloom – Only ever happens in new tanks when free floating heterotrophic bacteria begin to populate. The fix – You just need to “Ride this one out” as it is just part of the nitrogen cycle. If you’d like to understand this in more detail refer to the link below as it is the only website I have found that gives a semi-detailed explanation of what is actually going on. https://www.thesprucepets.com/bacterial-bloom-1380092 Pic taken from Fishlab.com
Green Film on top of the water – This possibly a species of chlorella although I’m not entirely sure. This type of algae rests on the water surface. It does not make the water go green or stick to the plants or glass. Not very common but does appear if the aquarium is not “balanced” (to be unspecific). I’ve had to deal with this one a few times but it is very rare.
The good news is is that it was an easy fix. It literally disappeared the moment I introduced an Eheim surface skimmer. Don’t ask me how or why. Sorry no pic for this but the description should suffice.
Oedogonium – A green filamentous slime/very thin hair algae. I had this show up on a new piece of spider wood that I introduced to a brand new aquarium. Personally I believe the cause was a combination of things. A) unidentified and nonessential nutrients leaching from the new piece of wood B) Insufficient levels of Co2 in comparison to the amount of light and C) the tank did not have adequate biological filtration (a common issue in new tanks). There was essentially too many variables to give a definitive answer. Most websites indicate lack of Co2 and poor maintenance which is a pretty loose description of a cause for something so specific.
To fix: I dosed flourish excel daily according to bottle directions and eventually got it under control over the course of a few months. I also added some floating plants to diffuse the light load and lesson the demand for Co2 Pic taken from The Aquarium Guide
Fuzz Algae – A generic and unidentified term for algae that remains short and appears to add a fuzzy coating on the leaves of plants. Common in newly aquariums due to inadequate biological filtration and aquariums with high levels of decomposing organic matter, likely due to deficient plants that are struggling to grow and half-pie dying plus the over feeding of fish.
To Fix: Dose excel daily according to bottle directions. Remove sludge and anything that can hang around and decompose like old leaves and fish food. Reduce the bio-load in the tank by not overstocking it with fish. Remember plants that are struggling attract this stuff therefore fill you tank with easy and fast growing stem plants and practice good plant care by adding some fertiliser into the water or root tabs into the substrate. Using excel daily and having a steady current in the tank will also help significantly. Adding some floating plants will help by diffusing the light while the tank establishes itself into an environment that can sustain healthy plant growth thus warding off algae as that’s wht plants do when they are thriving. Pic taken from The Greater Washington Plant Association
Tips and Helpful Information
- Maintain good water movement. Either use power heads, Water pumps or get a filter that puts out a current. Unless you have fish that dislike a current, still maintain some sort of water movement.
- Don’t deprive your plants of nutrients by using phosphate and nitrate removers. Plants need phosphate and nitrate. Nitrate, phosphate and potassium are the three most consumed essential nutrients for plants. Without those nutrients they will eventually die. It is a common myth that nitrate and phosphate are the cause of your algae issues, yes nitrate and phosphate feed algae, but they are not the cause. Instead, focus on ensuring the essential nutrients are always available. If you try to starve the algae of nutrients you’re also starving your plants as well, consequently causing your plants to slowly decompose and become algae magnets themselves as they begin to decay. Also algae is better at consuming decayed organics where as plants are not. Ammonia is a result of excess decaying organics which is a known cause of algae.
- Plant fast growing stem plants like rotala rotundifolia, hygrophila polysperma and star grass around your slow growing plants like anubias. Healthy, fast growing plants produce algae inhibiting chemicals. This in turn protects themselves and the plants near by. Any tank struggling with algae needs easy and fast growing stem plants.
- Add some floating plants like Ludwigia Repens and Hydrocotyle Luecocephala if you have a tank that is completely out of control with algae. Remove them slowly as the tank starts to come right
- Plants need light, Carbon, Food, and a stable environment. Ensure that those things are in excess in order to rule out those things as a possible cause for your algae issues, since troubleshooting the cause of algae is a series of elimination. If you don’t inject Co2 then you can use flourish excel as a supplement as this helps counteract the existing low levels of Co2. Excel is not carbon but it is a growth supplement and has the added benefit of warding off hair algae. The level of light you provide must be compensated with nutrients and Co2 or Excel.
- Plants that are not being given the fundamentals are magnets for algae due to their cell walls degrading and leaching organic matter. Algae is attracted to anything that decays since this produces ammonia.
- Fish food and fish waste does provide nitrate and phosphate. Some low tech tanks can get away with nothing being dosed due to the plants finding the necessary nutrients elsewhere. I.e. tap water for calcium and magnesium-, phosphate in fish food, nitrate from the nitrogen cycle, potassium from fish food, iron from tap water. You can of course try this but if all else fails then you’ll need to add something. Start with root tabs as they are the easiest method to fertilisation. API and Seachem are my favourite brands followed by the DIY root tabs we stock. Sera also have a new root tab on the market which we are excited to try out.
- Don’t allow air bubbles to flow through your plants. It creates holes in the leaves and they don’t thrive, some may even die. I noticed that anubias in particularly cannot stand being near air bubbles and long term this is a sure method of killing it.
- If you are feeling overwhelmed from the amount of information regarding plant nutrients and dosing. Our no brainer pre-made Dry Ferts are always available at a cost effective price. Visit https://aquaticplants.co.nz/product-category/fertilisers/
- Don’t go rushing to the store to buy algaecides the moment you see algae. Read the descriptions of how to deal with each type of algae so you can make an informed decision before treating, as algaecides are toxic to your environment and will ultimately set you back in your goal to achieving a functioning and established eco-system.
- Put your lights on timer!! Run them for approximately 8-12 hours a day. Some people say that doing a siesta period helps prevent algae. I have not noticed any difference doing this personally.
- Aim for white lights not yellow or warm colours.
- Don’t let sludge and organic matter build up in your tank
- Don’t over stock the tank
- Ensure your filter flow rate is sufficient for the tank size
- If you are running a cold water fish with goldfish, consider adding a heater to bring the temp up to 23 degrees (max temp for healthy goldfish). This will keep your plants growing as opposed to going dormant yet still be safe for your cold water fish.
- Keep sunlight off the tank – If you are hell bent in using sunlight as a light source, consider using shade cloth to diffuse it. This will be a bit of trial and error to figure out percentage of shade you’re after.
- If you build a fish pond, consider adding multiple depths inside it so that when the water heats from the sun it is able to heat the shallow areas quicker than the deeper areas. This will provide natural movement because of the different densities in both temps causing the hot and cold areas to collide and thus prevent stagnation. It is wise to build ponds in areas that get some shade a varying times of the day as a full day of blazing hot summer sun would be a volatile and unpredictable position for a pond.
- Ponds need plenty of plants to become functioning eco-systems
- It is a common misconception that nutrients create algae. Deficient plants will be algae magnets therefore focus on giving the plants everything they need as opposed to depriving the algae of nutrients. If you deprive the algae you will also deprive the plants. It’s a catch 22 situation. The goal is to have healthy plants therefore focus on giving the plants everything they need to thrive. Healthy plants will combat opportunistic algae spores resulting in little to no algae.
- Don’t ever use marine sand/coral sand or add crushed oyster shells to your tank. These will all raise the PH significantly and cause nutrient lock out. Nutrient lockout is when the nutrients are present in the tank however the plants are unable to absorb them due to incorrect PH. The ideal PH for a planted tank is between 6 and 7 with 6 and 6.5 being more favourable. Even if your tap water is above these ranges, don’t worry about, as the nitrogen cycle will push the PH down providing you keep your tank fully cycled.
- When plants come into a new environment. I.e. you just purchased them, they will need to acclimatise. They shed their old growth and grow new stuff. This even includes the roots. As this happens you need to remove the old growth slowly over time until you can see the plant has established itself in your aquarium. Don’t uproot the plant however.
- Any old looking algae riddled leaves, remove them ASAP! They won’t repair themselves therefore it is of no benefit leaving them in your tank. Removing old unattractive growth will encourage new growth. Make it so that the plant does not have to give energy to leaves that it should no longer have to sustain. Focus on new growth, not repairing the old.