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Q11104 - HOWTO: How to Prevent Algae in Aquarium Systems by Daniel S., Reef Squad

Sooner or later, every hobbyist has to deal with nuisance algae in the aquarium. Unchecked, the nuisance quickly turns into a plague, leading many saltwater aquarium aquarists to start over or leave the hobby all together.

There is no reason to quit the hobby over algae. While the issue can seem complicated, the general recipe for success is simple, and we're going to give it to you. Many aquarists fail because they don't ask the right question. Instead of asking, "How do I get rid of nuisance algae?" The question to ask is "What causes nuisance algae?" Once you know the cause, you can get to the root of the problem. The answer is a bit lengthy, but it will make all the difference in your aquarium.


Aquariums Remember an aquarium is a closed system. This just means that everything that goes into the system stays in the system, until it is removed. If more nutrients are going into the system than coming out, nutrients will build up.

Algae is the result of a nutrient imbalance. Basically, more nutrients are going into the aquarium than are being removed. These extra nutrients are feeding the algae. The longer the imbalance continues, the more the algae will spread. Seen this way, it is easy to understand how nuisance algae can quickly become much more than a nuisance. This is why it is important to first deal with the imbalance.

"You don't have an algae problem. You have a nutrient export problem."



So where do the nutrients come from? Simply put, every living thing in the aquarium, and everything put in the tank to feed them. Fish need food to survive. Fish waste goes to feed invertebrates, and so on. Anything not used by the wanted organisms and not removed from the system will go to feed unwanted organisms. This is why it is very important not to overstock or overfeed the tank.

It is also important to manage how you feed the tank. Do not feed more than your aquarium fish can eat within a few minutes. Turn down the flow so that the food doesn't end up getting blown into the rocks or sand, where it will rot. It is better to feed small amounts twice a day than to feed a large amount all at once.

Tip: When feeding frozen food, thaw the food in a cup of tank water, and then strain out the liquid before feeding. All of that binder and juice is just algae fuel.

Be sure you are using pure water. If you are not, you are just adding fuel to the fire. Tap or well water is often loaded with phosphates and nitrate, which go straight to feeding the algae. If you are using polluted water, you are fighting a losing battle. Setting up a reverse osmosis/deionizing (RO/DI) water filter will make a world of difference. Read this article to learn more.


Frozen Food
Tangs Once in the aquarium, nutrients must go somewhere. We want to feed the livestock, like fish and corals, as much as possible with as little waste as possible. Wasted nutrients just end up feeding algae. So how can we process the nutrients in the system better? Janitor organisms, or the clean up crew, are an important part of a healthy reef. They gobble up uneaten food and dead organisms. They also eat algae off of the glass, rock, and sand, keeping the aquarium clean. A diverse clean up crew will go a long way to keeping your system algae free. Why do the work of cleaning up if you can introduce an animal to do it for you? This also goes for herbivorous fish like blennies and tangs that will gladly eat up many different forms of algae.

Tip: For more information on herbivorous animals, and further information on algae control, pick up a copy of Algae: a Problem Solver Guide, by Julian Sprung.

Biological filtration also helps process nutrients. Deep sand beds slowly remove nitrates. Refugiums 'bank' nutrients in the algae to be pruned regularly. However, be careful of trickle or wet/dry filters. While great for freshwater systems, most reef hobbyists feel that wet/dry filters lead to a constant buildup of nitrates that is difficult to deal with.


There are two main weapons for removing nutrients, filtration and the dreaded water change. Be sure you have the right filtration for your system. Make sure your protein skimmer is strong enough, and that it is frequently cleaned and serviced. A collection cup, cleaned twice weekly, is likely to double the performance of a skimmer cleaned infrequently. As grime builds up on the riser tube, it gets harder for the waste to rise up and into the cup, reducing performance.

Mechanical filters are fine to use, as long as they are regularly cleaned. Fish waste left on the rock or sand bed may get eaten by the clean up crew. Fish waste and uneaten food sitting in a filter sock or sponge is just rotting, releasing unwanted nutrients. If mechanical filters are not rinsed/changed frequently, then the buildup of waste becomes fuel for algae.

Collection Cup

Tip: This also goes for canister filters, and is why we do not usually recommend them for a reef tank. Unless the mechanical media is rinsed/changed very often, they do more harm than good.

There is no replacement for water changes. They are an important part of aquarium keeping. Generally, the more often you change the water in your system, the healthier it will be. Many algae issues arise because the fish are swimming in their own waste. As Anthony Calfo likes to put it, "the solution to pollution is dilution." We don't have the space to cover water changes here, but if you're interested in more details, check out the article and video on aquarium water changes here.

Tip: Right before siphoning water out, take a powerhead and blast the rocks with it. This will knock uneaten food and fish waste back in the water to be removed.


Algae So far, we've been speaking of nutrients in general terms. To be more specific, when it comes to algae we are mostly worried about nitrates and phosphates. If nitrates and phosphates are kept in check, the algae will be too. The methods listed so far will help prevent these from building up, and be 95% of managing them. Next we're going to talk about removing them. Most people focus on algae removing products, while overlooking the things already mentioned. A balanced approach is what will make the difference.

Manually remove as much algae as possible, as often as possible. Remember that algae "banks" nitrates and phosphates inside their bodies. As they starve, wither away and die, they release these nutrients back into the system, feeding other algae. This is why, once the excess nutrient problem is dealt with, algae continue to survive for some time. Every time you remove algae from the system, you are removing banked nitrate and phosphate. This is why a refugium works.

Tip: Remember, even if your tests show no nitrate or phosphate, the presence of algae means they are there in excess. Nitrate and phosphate are just invisibly 'banked' in the algae, needing to be removed from the system.

High nitrates don't just lead to algae problems. They risk the health of everything in the aquarium. One way to reduce nitrates is a sulfur denitrator. A denitrator is a bacterial filter that lowers nitrates through biological processes. They are expensive, but useful, especially on predator tanks. There are also additives that help lower nitrates, like AZ-NO3 and Microbacter7.

Finally, phosphate control is the most important aspect of algae control. Without excess phosphate fueling the problem, algae will disappear over time. I recommend a two-pronged attack against high phosphates. First, use a liquid phosphate remover like Aqua Vision's Phosphate Solution. This will quickly bring the phosphate level down to undetectable levels. Then, install a phosphate reactor and media, like Two Little Fishies Phosban Reactor and Phosban. This will starve the algae. As the phosphates begin to rise (usually after a month), re-dose the liquid phosphate solution to take it back down to zero and change the media. Check out this article to learn more about setting up a media reactor.

Tip: Make sure your phosphate test kit will register low enough. Phosphate on a healthy reef should be around 0.03ppm.

So, there you have it.

Phosban Reactor
If you have algae, you have a nutrient problem. You need to examine your husbandry to determine why more nutrients are going into the system than coming out. We've listed the most common reasons, but you may find others. Fix those problems, and then consider media to help maintain low levels in the system. That's it!

It will not change overnight, because it did not happen overnight. Nutrients may get bound up in the sand and rock, and need time to slowly exit the system. Follow the recipe, attack the root cause and the problem will go away. As always, feel free to contact the Reef Squad if you have any questions. We're here to help you succeed.

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Approved Comments...
Yes this info gets well to the point ,nicely put together very informative & great to have it written into understandable fish keeper language. Approved: 5/13/2013
Very informative and well researched. Approved: 11/5/2012
Very informative and guided me step by step. Only thing missing would be a picture or two. Great article. Approved: 11/4/2011
I think the differences between reef, freshwater, and freshwater planted aquariums needs to be made. This article is primarily for reefers or non planted freshwater hobbyists. Most of these principles do not apply to algae control within a planted tank. Otherwise, good article Approved: 10/11/2011
I disagree with a previous post that this was too scientific. The article was well written and informative. Approved: 3/30/2011
I agree and wouldve rather had gotten a refugium for my 29 gal reef tank(a gift and I wouldnt have gotten anything less than 150gal.but for now) but my LFS begged to differ and said to use the cannister filter system which are better. I do notice I have to rinse often to keep algae in check. Especially when my clean up crew died over time I noticed to have to do more and more H2O changes till I got some more cleaning crews. Knowing my system I swore the cannister filter was the prob. but LFS said that was absurd. This article clears up what I have suspected all along. My LFS blamed it on lights, water, etc which I know for me wasnt the problem. My cousin has a refugium and doesnt experience any of the constant husbandry I am subjected to. Thank You for the up front helpful answers. Approved: 3/28/2011
I want more solutions, especially for nanos. Approved: 3/2/2011
Dear Sir,your article was helpfull in me understanding more about algae problems. Iam setting up a CoCahoe minnow closed system. curently i have 7-45gal.aquariums,set up in line.Iam going to be running (Iwaki md-70RLT pump) i would like your in put as for iam recherching the idea of installing a (Coralife Turbo Sea 1740p)pump from your company,in the next 2-weeks.The CoCahoe minnows can not live when oxygen levels get below 4ppm.& need brackish warter for best results i look forward to trading with your company.thanks Michael C. Luke EDITORS NOTE: Please contact us at for help. Approved: 2/28/2011
Thanx! Approved: 2/28/2011
It was very informative but too scientific for me, cut to the chase and summarizes it for me. Give others who have time to read and study a place to go if they want an education. Approved: 2/28/2011
It was great! Approved: 2/27/2011
OK Approved: 2/27/2011
You guys are the BEST!! Approved: 2/26/2011
simple and down to the root. Approved: 2/26/2011
Found article to be helpful, but would have liked to know if solutions were the same for freshwater. Approved: 2/26/2011
Very good ideas and thankyou. Approved: 2/26/2011
helps a lat Thanks Approved: 2/26/2011
Very informative. Wonder if process is the same for fresh water tanks? Approved: 2/26/2011
Helpful. Put simply enough to understand and make complete sense. Great for novices as well as a reminder for the more experienced. Thanks! Approved: 2/26/2011
GOOD INFO, GOOD TOPIC Approved: 2/26/2011
Thanks Approved: 2/26/2011
Good content, could use more solutions-or more so ways on how to install and what to do with the equipment Approved: 2/25/2011
Good content, could use more solutions Approved: 2/25/2011
I am glad to see you address the root of the algae problem - nutrient imbalance. Some comments. Hobbyist phosphate kits dont measure organic phosphate - even a system with a low inorganic phosphate reading on a hobbyist test kit can still have an algae problem due to excess phosphates. Also, while it may be contradictory to a goal to sell more product, proper feeding and stocking and water changes are the real key here. Nitrate and phosphate reducing chemicals are a band-aid for a husbandry shortcoming and can have harmful side effects of their own. You mention solving the problem before using media in the summary but I would consider chemical approaches to be a short-term fix to help get a tank back under control. Approved: 2/25/2011
As much as I commend those who do salt water tanks, I do fresh and would have liked this article expanded to cover it as well. In fact, it would have been nice to compare, in a single article the differences and similarities to the problem and their solutions. Approved: 2/25/2011
For planted tanks, the content of this article is 10 years out of date. There is no way to limit nutrients to inhibit algae. Plants should be presented with conditions for optimum growth and instead LIGHT should be limited to control algae. Approved: 2/25/2011
my tank has been up quite a few years and over the last 2 ears i have been battling algae. Thanks for this article. Approved: 2/25/2011
I always thought that the frozen food juice was nutritious, but now I know it is! For the algae not the fish! Approved: 2/25/2011
It is good infor. Approved: 2/25/2011
THANK YOU. Ive been struggling for a year to get a pesky return of algae from smoking my corals. You nailed it, and Im going through step by step to correct the OVER nutrient problem. Approved: 2/25/2011
good answer Approved: 2/25/2011
The only reason I didnt give the article a 10 was that, while your method is the best way to keep algae in check, you didnt say anything about algae eater fish. Sometimes nutrients can get out of balance despite your best efforts and having one of these little guys in the tank can take up the slack until you can get things back under control. I let my tank get totally out of control once upon a time and, as you say, I was ready to rid myself of the whole hobby. It was then that someone said to put one of these amazing little fish in the tank so the problem wouldnt get worse while I worked on a more permanent solution. After he had been in there for about 2-3 weeks I almost didnt have to look for a more permanent solution. And we are talking about a tank that you could barely see into when I first put the algae eater in there. So while your method is the best, Im surprised you didnt mention these amazing little fish as a good plan "B." Approved: 2/25/2011
Article Details
Created on 2/22/2011.
Last Modified on 2/28/2011.
Last Modified by Administrator.
Article has been viewed 51427 times.
Rated 9 out of 10 based on 141 votes.
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