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Algae Control!
Well, Congratulations!! You made it, you did it, you got the plague!

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Something tells me you finally got more light, you're thinking about CO2, you are fertilizing, your tank's full of plants, and now all of a sudden BOOM there is algae. Green water, green spots, green hairs short and long. It's everywhere, growing at alarming rates, covering the plants you set out to nurture and adore, it is stiffling! Well, sorry if I do not sound surprised, but this happens all the time, and yes, even the best of us have it or had it. Not to worry there are approaches you can take to remove this infestation. First lets dispel a few myths, or at least list some.

  • Algae killers take care of it.
  • Liquid Fertilizers cause it.
  • Terrestrial Fertilizers cause it.
  • Bleach everything.
  • Heating cables in the substrate will get rid of it.
  • Wrong gravel, UGF, Power Filters, lack of or presence of CO2.
  • Salt will help.
  • Laterite will make it appear.
  • Lights are to blame.
  • More water changes, yeah that's it.
  • Phosphate absorbers, naa.
  • The Iron in my tap water combined with what's in the Fertilizer.

These are all the answers, or are they? These are the excuses I have heard again and again. Are there any truths in these "Words of Wisdom"? SURE. Let me start with one assertion, the driving force in all algae control measures, the one truth that most of the advice stems from.

Algae Control is all Nutrient Control.

That's it. Pretty simple right. All you have to do is maintain the correct "Balance" and everything is great. Well this is at least the challenge. It is all about details. Like anything else in the hobby, details, the little things, that's the key. We can talk of individual factors that may be attributed to the presence of algae, and your local conditions may favor one imbalance that makes your solution a little different then say, mine. None the less, in the end it still was an imbalance that was the cause of the problem, and rectifying that solved the algae bloom.

Now you are here because you have algae and want to rid your tank of this annoying presence. Wether you're running a fully planted tank or a fish only tank the same rules apply. However I am going to gear my discussion towards the plant tank people. The fish only people can always just turn off the lights for a few days. The aquatic gardeners however are not as fortunate and their task is a little more detailed, but not very hard. This page will also take the approach that you are involved in the maintenance of the tank. I am not one for setting up general rules to blindly follow and therefore I prefer to start from scratch. But that is just me.

Let me start with a link. There is a paper written by Paul L. Sears and Kevin C. Conlin, their take on this issue is the one I follow. They performed a case study on the effects of different nutrients on algae growth rates. Their conclusions are sound and are what I base my approach on to this day. For those of you who would like to read their work and make your own decisions their case study is available online.

Algae is a plant and you just created an environment perfect for plants. So, well, it makes sense then that the algae is doing well in the environment you have carefully created. Aquatic Plants require 4 basics to grow: light, nitrogen, phosphate, and potassium. You've stuffed all kinds of light up in that hood, your fish are excreting plenty of nitrogen and probably phosphate as well, the only thing that is not abundant is Potassium. Now you ask, yeah so, what then, if the plants I want and the algae all grow in the same environment, then it's a no win situation. This is not true, there are differences. All plants are not the same. Algae are efficient feeders, they are also very advantageous growers adapting to use what is available. But if the required nutrients are made unavailable to the algae well, they go away. There are however certain methods that allow the higher plants to out compete the algae for available food sources, and this is what we want to take advantage of in our fight against algae. That brings me to my next statement.

Use the higher plants to out compete the algae.

If we cater the water parameters to favor the higher plants they become nutrient magnets. The higher plants will consume the majority of the nutrients leaving little behind for the algae to survive. Now that is not to say there will be no algae, but without enough food, the algae will be held in control. There is always going to be algae in the tank, it came in with the plants, but proper management can keep it at bay. Lets take a look at the main nutrients.

Trace elements
2-4 watts per gallon.
Trace to 25ppm
This has a broad range for interpretation. Full spectrum is the best, but intensity is more important. More than 12 hours is unnecessary. This is pretty straightforward. The ammonia and nitrite levels should always be unmeasurable. And the Nitrate levels should be kept below 25ppm. Same as nitrate. Since this and nitrate are your two main concerns, keep this at a minimum. Trace amounts are all that's needed. And it is the easier to control. Potassium has never been associated with algae blooms. Therefore there is no real hard number here. Keep the levels up, but there is also no real test kit for this one either. I dose it regularly. The trace mix recommended is in the PMDD link. The measure for all trace elements uses Iron as an indicator. Keep the Fe level below 0.1ppm or algae will like you.

With the above table in mind the general recommendations can fall into place. OK, in a plant tank we will have lots of light. This is a given and needed to keep the plants happy. So there is no leeway there right? Wrong. Remember details are key, and therefore we can make some minor adjustment here that will favor the plants. Again algae is very opportunistic and will absorb just about any form of light. But plants predominantly use blue and red. The orange, yellow green and indigo are useful as well, but not as important. The plant lights, gro-lux, and other "grow" bulbs are mostly red and blue and shed a funny purple hue. Now cool white and a lot of cheap aquarium tubes are heavy in the yellow/green spectrum as that is one of the best we can see. However plants are green and that means the majority of the green light is reflected and the others absorbed. So the use of a nice full spectrum light and a Plant light are of a little help here as most of the light works for the plants.

I like to discuss (N)itrogen and (P)hosphate at the same time as they are inter-related when it comes to algae control. If our plants were grown emersed (above water) we wouldn't care, but they are not. If we didn't keep fish, we could control our dose of N & P, but who doesn't keep fish. Some keep very small populations of fish to keep their N & P in check and then control their additions. Here is where the fish only people have their issue too. Outside of the fact that they can always turn off the lights, fish only tanks generally have a ton of excess N & P. And in the fish only case we can do increased water changes. But in a plant tank we already do them every other week right?:) So what's next. Get the plants to eat the excess. Or is it excess? Well if there is algae it is an excess. Balance is what you want. You need to get the plants to consume the available Nitrate and Phosphate and keep the levels in check such that there is not an excess. Now the other fact is that if you keep at least one of them in check you will go a long way for algae control. If either N or P is limited, in short supply then the algae will be hurting for food. Now if you have enough light and there is not too many fish, and the nitrate levels are up, the PMDD methodology calls for an increase in Potassium.

So Potassium(K). I start with the recommended dosage as called out in the PMDD recipe then augment from there. The baseline recipe is a good start, then you can add more as needed. And remember an excess of K does not lead to an algae bloom. What the exact concentration does to the tank I am unsure of as of now. But my method has been working well for a few years now. You increase the K dosage as needed to reduce the nitrate levels. Although I find the PMDD baseline to be a pretty good value, my only real increase is during water changes. I add about 1/8 teaspoon per 10 gallons of replacement water. Now there are other fertilizer methods and they will all call for slightly different approaches. But the basic call for potassium is something that seems to be somewhat overlooked in some fertilizers. A lot of liquid fertilizers are trace mixes and lack potassium.

Trace elements are the last factor. Most mixes used have the correct balance for all the trace elements. This way we can monitor one element to gauge the correct concentration of the others. Basically the assertion is that if the iron levels drop then it was consumed and the other microelements will be consumed in equal proportions. So we monitor the Fe levels and maintain them below 0.1ppm. Also if there is an excess of any one trace element left over its concentration will be reduced through regular water changes. So the trace element management is pretty simple. I myself only measure Iron if I suspect an excess for one reason or another. But I also watch the color of the red pigment in plants to indicate enough. But with algae control we are more concerned with an excess of iron. Although as I have said before, balance is key. A lack of microelements or any one of them can stunt the growth of the plant and lead to a decrease in the uptake of other nutrients leading to an excess of something like nitrate. Now this reminds us that balance is concerned with all nutrients, not just one.

So a balance means you will need to pay attention to all these conditions at the same time. That sounds like a daunting task, but once the balance is achieved it is not a very fine line that is easy to loose. You can maintain a tank without measuring all these parameters all the time. Once the tank is there and you get an algae outbreak you may need to measure a few parameters to get an idea of the problem, but with the inter-relationship of these ideas in mind the solution will be obvious. Keeping all the values in check will all but guarantee success. But usually the balance is not an immediate thing but something that requires a tank to break in for a few months. The break in period is the most crucial. After that following a few guidelines will mean a controlled algae environment.

Lets cut to the chase. What does this all mean? Well like I said the key here is nutrient control. A balance of all the details that will produce an environment which stimulates the plants and hopefully allows them to consume enough excess nutrients to keep the algae at bay. Therefore I have a few recommendations that will help achieve this condition. Doing all of these is not necessary, but the more satisfied the better the results.

Helpful tips towards algae free plant tanks.

Provide 2-4 watts of full spectrum light run for about 12 hours a day. A Timer is helpful to maintain consistency.
Maintain a fish load, feeding schedule, and water change schedule that will keep the NO3 levels below 25ppm.
Phosphate levels should be minimized. There is plenty of P in fish food and additions are rarely needed. Watch out for pH buffers, many use phosphate.
Potassium is one of the most overlooked additions. Adding K on a regular basis will increase the plants ability to uptake other nutrients.
Trace elements are very helpful. In low light conditions plant uptake rates are slowed and it can be easily overdosed so monitoring of Fe levels are highly recommended until the hobbyist becomes comfortable.
Fertilizing the substrate is advantageous. As long as there is no UGF, additions of Nitrogen and Phosphate to the substrate may keep them out of the water column and available to plant roots.
The use of a phosphate absorbing resin in the filter in times of nutrient imbalances can be helpful.
The incorporation of fast growing plants especially in the beginning will help consume excess nutrients keeping the water born food source minimized.
The use of substrate additives will produce a favorable environment for the plants roots. Laterite is highly recommended but there are other sources.
Water changes ever two weeks help dilute excess nutrients and maintain a clean environment. To many water changes will not allow the water to stabilize and can be just as bad.
Knowledge of your tap water conditions can help you decide if any other additives are needed like Calcium or if you need to leave something out of your fertilizers.
The addition of CO2 can be a major advantage to stimulate plant growth. Additional CO2 will substantially increase plant growth.
Daily additions of liquid fertilizers assure a consistent availability of what the plants need. Dosages need to be watched so not to overdose, but Fe can be made unavailable in only 24 hours.
General cleanliness can be very helpful. The prompt removal of dead and dying leaves and other debris can help contain the release of unaccounted nutrients.
An algae eating army can help keep the algae in check. There will be algae and fish snails and shrimp can help control it.

Sorry, you didn't get one simple answer like more water changes or a different food or and algae killer. But that is because this approach does not treat the symptoms, it helps eliminate the conditions that cause algae. When we keep the water born nutrients limited, especially phosphate and nitrate, algae will have a hard time getting a foothold on your tank. And the best, natural, long term, low maintenance approach for this is make the plants grow like mad. You need to control the input of plant nutrients including and most importantly the ones provided by the fish. The best environment for the plants yields a great opportunity for algae, so limiting the N or P in the water column will greatly help in limiting the algae growth. Also to be considered is the presence of Fe. Iron can almost spur on algae as fast as an excess of N & P, but without the N & P the algae will still have a hard time Fe or not. If a plant doesn't work for you, try another. A tank full of hard to grow plants will undoubtedly end up with algae. Start with a lot of fast growers and then over time replace them with slower growers and those that may be harder for you to grow. But if you have enough fast growers, one or two problem plants will not bring about algae. Learn to be observant of the tank's condition. If you see a possible nutrient imbalance in the tank and can identify it early you will be well ahead of the game.

Reader Comments Comentário

I have found another method for algae control on the Dennerle website ( They recommend to switch out the light for 2-4 hours during the day, as a sort of afternoon nap. The rhythm they recommend is 4-5 hours light in the morning, then 2-4 hours without light and again 4-7 hours light in the afternoon or evening. Plants and fish don't mind, but algae don't like the break. I use this method for my 180 liter tank, that has been running for seven months now and so far I've had no problems with algae. I don't know if this is due to the fact that I have Otocinclus and Amano Shrimp in my heavily planted tank, or maybe it is the combination, but this method certainly does no harm.

Contributed by Christina Magiera

I bubble highly ionized air (created from cold plasma discharge tubes) into the aquarium and also the outdoor koi pond. The results are remarkable although the science behind this is fuzzy. It has something to do with ion competition between Ca, N, K, etc. Effectively, the excess nutrients and raw fish waste is converted into higher plant nutrient compounds. Fish are healthier, less algae and the plants grow bigger and faster. Only problem is that the plants can eventually wither (about 2 years) if the nutrient source is lowered eventually by such rapid and unsustainable plant growth rates.

Contributed by trapper

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