Introduction to algae issues

What induces freshwater algae in planted aquariums?

Algae will flourish in unbalanced aquarium systems. What causes these unbalanced conditions?

It is of great importance to feed our plants on regular bases a well balanced diet with NO3, PO4, CO2 and other macro and micro elements.

In the past many believed that NO3 and especially PO4 can induce algae. It has been proven numerous times that these nutrients (even if overdosed) can not create algae issues. Actually the more we dose the less algae we get.

Plant nutrients in general have nothing to do neither with algae issues nor with fish/shrimp issues (dead/sick fish/shrimps) in planted tanks which are regularly dosed with fertilisers!

The question is; “Why do I get algae even though I dose NO3, PO4, CO2 and other nutrients on regular bases”?

The worst mistake many do in such cases is they start reducing nutrients out of fear that these nutrients might be creating the algae issue. Such nutrient reducing method will induce algae even more!

Let’s name the real reasons behind algae issues in planted aquariums which are dosed with nutrients on regular bases:

  1. Low Oxygen level
  2. Insufficient water circulation
  3. Organic build-up
  4. Un-cycled aquarium

Low Oxygen (O2) level can be caused by overstocking, high water temperature (summer time), dirty filters, overfeeding, weak surface agitation.

Insufficient water circulation can cause poor nutrient transport. Even though we dose enough of CO2, NO3, PO4 + traces the water flow has to be strong enough to deliver all those nutrients to the plants. Improve over all circulation (stronger pumps, more pumps).

Organics tend to build-up over time with feeding, fish-waste, rotting plant leaves, etc… Decomposing bacteria needs ample supplies of Oxygen in accordance to decompose Organics into inorganic compounds like NH4, NO3, PO4, and CO2 which plants can use up.

Shredders like shrimps and snails can help a lot in organic recycling. Bacteria can’t decompose bigger organic peaces fast enough. Shrimps and snails will eat dead plants leaves, un-eaten food or food trapped in gravel preventing them from rotting slowly.

Keep good O2 levels by creating a moderate surface agitation, keep the filters clean, keep good circulation, remove un-eaten food, remove old plant leaves, perform regular water changes, stock the tank with shrimps and snails and perform light gravel vacuuming every so often.

Un-cycled aquariums don’t have enough of beneficial bacteria to help in recycling organics and therefore Organics and NH4 might tend to build-up inducing algae. Cycle the aquarium by using following methods:

  1. Fishless Cycling
  2. Silent Cycling
  3. Jump Start
  4. Dry Start (I will mention this one in the following article since this one is best suited for planted tanks with nutrient rich substrate/soil).

Please do not reduce nutrients like NO3 and PO4 in planted tanks to fight algae! By reducing them you will only induce algae even more! NO3 and PO4 can cause algae issues ONLY if they are MISSING!


Algae Control (the article)

Non-planted aquarium
Excess organics and ammonia/ammonium levels will result an algae break-out. Over feeding and over stocking is the most common reason for water quality to go bad. Performing weekly water changes (25-50%), substrate vacuuming, creating a moderate surface agitation for gas exchange (good O2 levels), maintaining sufficient water flow/circulation and cleaning the filters regularly are the best solutions in preventing algae issues. The ammonia (NH3), ammonium (NH4) and nitrite (NO2) levels should be at 0ppm. Nitrate (NO3) levels should be kept below 30ppm. Phosphate (PO4) levels should be kept below 0,5ppm. Lights should be at no more then 10 hours per day. Note that algae favour strong lights so placing the aquarium away from the window is a good idea. Direct sunlight will likely cause an algae-breakout. Algae eating army will help a lot in combating certain types of algae.

Planted aquarium is a bit more complex, because there are not just fish to take care for, but plants also. It is true that plants will uptake the ammonia/nitrAte/phosphate and keep the water chemistry in high quality. But what happens when you suddenly experience the worst algae out-break in a planted tank?! You will ask "but how is that possible"!!!

What induces algae in planted aquariums?

Some people state that algae will flourish in aquariums which contain lots of nutrients like NO3 and PO4 and they try fighting the algae by reducing those nutrients just to discover soon after that reducing nutrients only leads to more algae issues.

In heavily planted aquariums the fish waste alone doesn't provide enough nutrients which plants require to grow healthy without algae issues and for that reason we rather dose nutrients. Plants (like us) require balanced diet to be able grow healthy.

Lets mention the real reasons behind (most of ) the algae issues;

1. Uncycled aquarium

Most people get algae in the first 2 month since the set-up. Newly established aquatic systems lack in beneficial bacteria which helps in balancing the system. Such bacteria is involved in organic decomposition, nitrification, denitrification, etc... To avoid such algae problems in the begining I advice using the Dry Start Method (by Tom Barr).

Since plants grow much better in nutrient rich substrates ideally soils should be used. (E.g. potting soils, commercially available aquarium soils)
Soils also support various beneficial bacteria (
chemoautotrophic, heterotrophic) which are involved in the decomposition of organic compounds, nitrification/de-nitrification, reduction and oxidation of heavy metals and gasses into plant nutrients. This means that using plain sand or gravel would be a poor choice for establishing a proper environment for aquatic plants especially in Low-light Low-tech aquariums.

Potting soil (or commercial aquarium soil) is terrestrial (exposed to O2) and has to go through a very sudden change. Once saturated in water O2 levels decrease rapidly used up by the bacteria.
Bacteria use O2 during organic decomposition. At the start the soil once submerged will release lots of nutrients into the water column.
The soil has to settle down before flooding the tank. With this method we can avoid unnecessary algae blooms and water turbidity.
Keep the soil saturated for 1 to 2 month (I wait up to 4 month). Note! Do not flood the aquarium yet. Add more water if it evaporates because the soil must remain submerged at all times to convert (soil cycling) into a settled aquatic soil which the plants require. It is important to wait to ensure sufficient bacteria development involved in nitrification of Ammonium to Nitrates, avoiding NH4/NO2 spikes which are very toxic to fish and crustaceans.

After approximately 2 months it is really worthwhile waiting, the tank can be flooded. Once the aquarium is filled with water, flush it out!
We do this because the nutrients which diffuse out of the soil into the water column might cause unnecessary algae blooms.

If you are extra cautious you can repeat the flush-out a few times. There is no harm in doing this but the water must be
dechlorinated before adding it to the tank.
NOTE; never add ice cold tap water back into the system. It should be tepid to start with. Set the heater to approximately 26’Celsius.
At this stage introduce all the plants you want to grow. It is best to plant heavily from the submerged start. Also it is good to plant lots of rooting plants. Plant roots will add Oxygen into the
rhizosphere to protect themselves from heavy metal toxicity and also by doing this the O2 enables the oxidation of the very toxic Hydrogen Sulfide gas (H2S) converting it to harmless salt HSO4 and the oxidation of Methane gas to CO2 and water. The plant roots will prevent soil Redox from becoming too low.

2. Insufficient water circulation and surface agitation

It is of great importance to create sufficient water circulation and surface agitation in a planted Ecosystem.

Circulation will evenly distribute nutrients making them available for plants and bacteria. Aim for a circulation between 5-8 x of the tank volume per hour depending on plants grown and fish kept. Some prefer stronger currents while others weaker ones. Some aquatic gardeners use circulation of up to 10 x the tank volume per hour but they do reduce the water flow by using very long submerged spray bars which should be placed just below the surface.

Surface Agitation will insure sufficient gas exchange and will prevent the surface film from forming. Even though plants will provide lots of O2 through photosynthesis especially in CO2 injected systems it can’t hurt to add extra O2 via the surface agitation.
One should bear in mind that Oxygen is one of the most important electron acceptors involved in animal and bacterial metabolism.

At higher temperatures O2 levels decrease especially during the summer. When the temperature gets higher it is beneficial to create a strong surface agitation or add another power head for this purpose only. I have found that it is not the temperature that affects the fish/shrimp/plants during summer months but rather the low O2 levels. At higher temperatures the bacterial metabolism accelerates and uses up lots of O2 for nutrient recycling.

E.g. I live on the top floor and during the summer time the temperature of my tanks do go up to 31’Celsius. In the past I believed that this would harm fish, shrimps and plants. Now I know better. What I do under such extreme conditions is that I create a very strong (but no splashes) surface agitation in all my aquariums for good gas
exchange and I never experience any problems with fish/crustaceans or plants.
In planted aquariums keeping good Oxygen levels is as important as keeping good CO2 levels.
3. Unbalance between the light levels, CO2 and other nutrints (low CO2 and low nutrient levels)

For healthy growth plants require Carbon (C), Oxygen (O), Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg) and Sulphur (S) as the Macro Nutrients and Iron (Fe), Manganese (Mn), Zink (Zn), Copper (Cu), Boron (B), Nickel (Ni), Chlorine (Cl) and Molybdenum (Mo) as the Micro Nutrients.
In comparison to the Micro-nutrients plants require larger amounts of Macro-nutrients.
Macros and Micros can be added via commercially available products like
Tropica’s AquaCare Plant Nutrition N&P+traces and Seachem’s Flourish macro and micro fertilisers as well as dry fertilisers like KNO3, KH2PO4, Epsom salts, etc…

It is all about finding the right balance between the lights, CO2 and nutrients.
I have to draw a line here! There is a difference between dosing nutrients to an aquarium with only a few plants and heavily planted aquarium.
Plant density and plant growing rate is something to consider before deciding on the nutrient dosing methods.

Everything starts with the light. One can decide between using Low lights, Medium or High lights over the aquarium.
The light strength affects the plant growing rate. The stronger the light the faster the plant will grow and the faster it will up take the nutrients.
Deciding which light levels to use depends entirely on the aquatic gardener’s life style and goals.

Planted aquariums are complex and dynamic ecosystems, which hugely depend on us (the
Nature doesn't have much influence on them, and for that reason we are the ones pulling all the strings in leading them to an algae free/thriving planted ecosystem.

Plants need stable nutrient levels to thrive and grow lush. It is up to
aquarist to understand the planted aquarium ecology and influence this system by finding the right nutrient balance.

Aquarium plants can be successfully grown in several ways and most of it depends on the light. This is simple mathematics;
The stronger the light, the faster the plant will grow, and the nutrient uptake will be greater.

Less light = slow growth = slow nutrient up-take.

Aquarium light levels:

Low lights are between 1 - 2 watts per gallon (0.3 - 0.5 watt/litre)
Medium lights are between 2 - 3 watts per gallon (0.5 - 0.8 w/l)
High lights have 3 watts per gallon or higher (0.8 w/l or higher)

How to calculate the light level:

Divide the total aquarium light wattage with the aquarium volume (gallons or litres) to get the light level per gallon/litre.

e.g. Lets say the aquarium is 48 gallons (180 litres) and has 2 x 30 watt fluorescent tubes.
2x30 watt = 60 watts in total over the aquarium
60 watts divided by 48 galls = 1.25 w/g, or
60 watts divided by 180 litres = 0.33 w/l
meaning this is a low-light set-up.

Common planted aquarium methods are:

Low-light Low-tech

Low-light (non-CO2 injected) planted aquariums, where soils are used as the plants' main nutrient source. This is a low maintenance method, which requires very few water changes.

Low-light High-tech

Low-Light planted aquariums where CO2 is used to stimulate the plant growth. This system will depend on extra fertilising and often water changes to stay in balance

High-light High-tech

High-light planted aquariums were CO2 is injected to stimulate the plant growth. Higher light levels provide plants with a huge amount of energy promoting luxurious lush plant growth. This is the common method used for creating stunning looking
aquascapes; (Aquascaping Competitions)

Which method suits me best? you might ask

This depends on your goals and your life style.

1. Lets say you have a very busy life; long working hours, studying, kids, etc... and don't have much time left for often aquarium water changes.
In this case, it is best to choose the Low-light Low-tech planted method, which needs only 5-6 water changes per year. For Low-tech tanks I dose nutrients once a week e.g. Tropica Plant Nutrition+ (read
plus) which contains NPK and traces 5ml per 50 litres. Even though plants can get most of the nutrients via soils we have to bear in mind that soils will become exhausted after approximately 6-12 month. To prevent this from happening it is beneficial to dose macro and micro nutrients via dry or liquid fertilisers once a week.

2. You have a tight budget, but would like to create a nice looking aquascape. Choose the Low-light High-tech method, meaning less light, less nutrients, inexpensive DIY/Yeast CO2 solutions, etc...
For this method I dose Tropica Plant Nutrient N & P + traces 1-2 times a week followed by a weekly 50% water change.

3. Or, your goal is to create a stunning looking planted tank for an Aquascaping Competition. In this case High-light High-tech method would be the best option. But to succeed in creating such a system, one has to dose nutrients often and do large weekly water changes to prevent nutrient over-dose. The best nutrient dosing strategy is known as the EI (Estimative Index) which was invented and popularized by Tom Barr.

For my 160 litres High-tech heavily planted aquarium with up to 0, 8 watts per litre I dose as followed:

*CO2 approximately 4 bubbles per second monitored via Drop Checker (25-30ppm).

Tuesday – (after the 50% water change) 1/2 teaspoon of KNO3, 1/8 teaspoon of KH2PO4 and 1/2 teaspoon of GH-Booster.

Wednesday – 10ml of Tropica Plant Nutrition for traces

Thursday – 1/2 teaspoon of KNO3, 1/8 teaspoon of KH2PO4

Friday – 10ml of Tropica Plant Nutrition for traces

Saturday – 1/2 teaspoon of KNO3, 1/16 teaspoon of KH2PO4

Sunday – 10ml of Tropica Plant Nutrition for traces

Monday – I dose nothing

With Tuesday it starts from the beginning (50% water change and nutrient re-dosing as followed above).

NOTE: Just remember, unbalanced planted tanks will lead to algae bloom, so e.g. choosing the High-light method, but not performing often water changes/plant pruning/nutrient dosing will lead to algae heaven.

Carbonate Hardness (KH) should never be under 4KH. Carbonates and Bicarbonates have the acid binding capacity. Carbonate Hardness level which is under 3KH doesn’t have a very good buffering capacity and therefore pH might shift drastically. If necessary dose Bicarbonates (Baking soda) to increase the KH.

Most plants can grow under all 3 light conditions if CO2 is not the limiting factor. For example it is believed that Hemianthus calitrichoides Cuba (HC) needs high lights to be able to grow into a foreground carpet. This isn’t true! This plant will do just fine under lower light conditions as soon as the CO2 is not a limiting nutrient. In CO2 limited systems HC like many other plants will grow upwards trying to reach over the water surface where the atmospheric CO2 is available. Many believe that plants grow towards the surface to get closer to the light source which isn’t true.
The most common reason behind plants growing like this or simply melting away is due to the limiting CO2 factor.
Of course under low lights plants will grow slower but with good CO2 levels they will eventually grow into the desired aqua-scape.

Insufficient aquarium hygiene and plant maintenance

Once the aquarium is maturing organic matter starts accumulating creating mulm, filters get clogged with particles, and plant bio mass increases to the point where tank maintenance becomes necessary.

With each water change it is good to perform light substrate vacuuming just over the gravel. No need for deep vacuuming in planted aquariums with many rooted plants. Like this we keep the beneficial Oxidizing Microzone (top layer of substrates) from becoming anaerobic (clogged with mulm).
The Oxidizing Microzone helps to convert toxic NH4 to NO3 and it keeps nutrients trapped in the substrate (oxidation).

Filtration will remove floating particles and help in nutrient recycling. External filters seem to work best in planted aquariums. One of the reasons they are a better choice than inner filters is that they keep all the collected dirt outside of the tank. Once the filter is opened for cleaning, all the dirt stays in it. On the other hand when taking the inner filter out of the tank for maintenance half of the trapped dirt leaks straight back into the aquarium. This should be avoided and for that reason external canister filters and hang on back filters (HOB) should be used.

Clogged filters will reduce circulation. Clean them regularly. How often depends on the pump type (external, inner) and fish bio-load.
When cleaning the filters make sure not to rinse them under tap water which contains chloramine. Such tap water can damage the beneficial bacteria living in the filter. Always rinse in aquarium water from the water change.
Under balanced nutrient conditions plants will grow better especially the fast growing stem plants. One should never allow them to grow to the surface. When this happen gas exchange becomes limited and low Oxygen levels might occur causing various issues e.g. algae, surface film, NH4/NO2 accumulation, stressed fish, etc...
Also, overgrown plants will reduce water circulation creating dead zones. Prune the plants regularly. This will not only encourage new growth but will make your plants look much better. The more you prune them the bushier they become.
Foreground plants should be mowed regularly. They tend to grow on top of each other creating a tick carpet. If the carpet is allowed to grow too tick it will start to rot from the underside and the whole carpet might float up (e.g. HC).

Partial water change is very important and should be performed weekly in Hi-tech and “Excel Only” aquariums. Like this we reduce excess nutrients which might have built up via extra fertilisation.
Hi-tech systems require frequent nutrient dosing (3x a week) and for that reason it is beneficial to do weekly water changes (50%) to re-set the system.
Low-tech aquariums require less water changes to prevent CO2 fluctuations. These systems need steady CO2 levels in accordance to avoid algae issues. Tap water is rich in CO2 and with each WC we add a fair amount of CO2 which plants will consume in just a day or two leaving them with low CO2 levels for the rest of the week. Fluctuating CO2 levels will very likely cause algae issues (stressed plants). For Low-tech tanks it is enough to do a 50% water change every 2 month. For that reason we rather under-stock with fish to minimize the organic build up.

5. Not stocking with enough shredders like shrimps and snails can cause organic build-ups causing algae issues
Certain fish and crustaceans can also help a lot in maintaining hygiene in a planted aquarium.

One of my favourite is the Caridina multidentata shrimp (formerly C. japonica) which was popularized by Takashi Amano. This shrimp is a very effective Thread/Hair algae eater. Besides algae it will also help to recycle dead plant matter and fish waste, breaking it down to smaller organic particles which bacteria can consume.
This shrimp also feeds on bacteria and micro-organisms preventing them from over populating the system.

Malaysian Trumpet Snail is very effective in aerating the substrate’s top layer keeping the Oxidizing Microzone aerated. It spends most of it’s time digging through the substrate in search for bacteria, micro-organisms and dead organic matter.

Otocinclus catfish which grows to just about 5 cm is a very useful addition in planted aquariums. This tiny fish will clean plant leaves from Diatoms and bacteria film.
Siamese Algae Eater (Crossocheilus siamensis) is the most effective fish in eradicating the Black Beard Algae (BBA). It grows to approx 14 cm and for that reason is not suitable for smaller tanks (fish requirements)

Neritina sp. Zebra is another snail worth keeping. It is particularly effective at eating the Green Beard algae and Green Spot algae which tend to grow on rocks and wood. Remember not to stock too many because they will start laying white eggs all over the aquarium which can look unsightly to some people. These eggs can’t hatch in fresh water.

Now that we know how to prevent algae, lets ID the most common algae in fresh-water aquariums: