Aquarium Algae Control

Updated August 12, 2019
Author: Mike - FishLore Admin
Social Media: FishLore on Social Media

So you have had your aquarium set up for some time now and you notice algae growing on the glass, rocks and ornaments in the tank. Why is this happening and what are some of the methods we can use to control aquarium algae growth in the aquarium?

First, aquarium algae is not necessarily a bad thing. Algae grows very easily when given the right conditions and some day we all may be singing the praises of algae. There is research going on even as you read this article for using it as an alternative energy source. Cool stuff indeed. But an abundance of algae growth in the aquarium usually means that something is out of whack. Overstocking, not performing enough partial water changes, overfeeding or feeding improperly, not changing out filter cartridges and not using pure water are usually the prime suspects.

Once algae starts to overgrow plants, corals and decorations it does make the tank look dirty and can distract from the beauty of your aquarium. Let's talk about the things algae needs to grow and how to eliminate or reduce these things so we are not constantly scrubbing the tank walls and having to clean the tank instead of viewing our fish, plants and inverts! You can use the info in this algae control article for both freshwater aquarium setups and saltwater aquarium setups.


Get a Phosphate Test Kit. This might be considered one of the most important nutrients for many kinds of algae growth. Phosphate (PO4) can enter the aquarium from tap water, fish food and supplements. One of the first things you should look at is how much you are feeding the tank. Are you overfeeding? Only give your fish as much food as they will eat in a minute or two. Are you defrosting and draining the juice from the frozen foods you use? These juices could be loaded with phosphates. Are you using food that are low in phosphates? Test them to see for yourself. At minimum, use a bowl to feed frozen foods and tilt the bowl at an angle so the juices drain to the low side and then spoon feed the chunks to the fish. Dispose of the frozen fish food juices down the drain.

aquarium algae

Activated carbon should be mentioned here too. Some brands have been reported to leach phosphates into the tank. Place a few pieces of activated carbon and pure water into a test vial, wait about 20 minutes to an hour and then test the water for phosphates. If that brand of carbon leaches phosphates try a different brand. Replace activated carbon on a regular basis, like every couple of weeks or so.

Are you using pure water for your aquarium? Reverse Osmosis (RO) and Deionization (DI) units can work wonders on algae problems, including reducing the amount of phosphate that enters the aquarium. Many consider RO and RO/DI units to be too expensive to be practical. But if you have several tanks or one large one or a reef tank setup one of these water purification devices are wonderful additions. You can even use RO water for drinking water and some actually prefer the taste of RO water over tap water. Ideally, you want PO4 to be undetectable with standard test kits.


Get a Nitrate Test Kit. nitrate (NO3) is something else that algae utilizes for growth. Nitrate accumulates over time in the aquarium. It's also used as a rough indicator of dissolved organics. To keep your nitrate levels in check:

Carbon Dioxide

aquarium algae gone wild

Limiting carbon dioxide (CO2) can help too. If you have a heavily planted tank, obviously, limiting CO2 isn't all that desirable. But in fish only freshwater and saltwater tanks you can increase the surface agitation while keeping the tank under stocked and dissolved oxygen levels should stay near saturation. Most of the time the flow rate in our tanks is inadequate, especially in saltwater tanks. Use common sense here. The goal here is to keep particles in suspension so they get picked up by the mechanical filter or protein skimmer, rather than breaking down inside the tank. If your power heads are preventing the fish from swimming properly or if there is a constant sand storm in your tank, you may have too much flow.


Get a Silicate Test Kit. Do you have a brown dusting on the glass every couple of days? Most like these are diatoms that can be the result of silicates in tap water. They (supposedly) can also be leached from silicate based sand. Some authors claim that RO and RO/DI units are only effective for a short period of time at removing silicates from source water. What to do? There are products that have decent reputations on the market for silicate removal. ROWAphos Phosphate Remover and PhosBan are two that come to mind. As you might have guessed from the name of these products they also remove phosphates. You can purchase an inexpensive reactor for using this type of filtration called the PhosBan Aquarium Reactor. It hangs on the back of the tank or in the sump. If you think you have a silicate problem one of these devices may be worth looking into.

More things to do to control algae...

Get a protein skimmer

For saltwater tanks a protein skimmer can be crucial to keeping algae growth at bay. Skimmers are loved by hobbyists because they completely remove dissolved organics and other proteins from the system via the collection cup. These are great tools for nutrient export. Once these items are removed they are no longer a source for algae growth. Keep your skimmer cleaned and maintain it regularly for best results. And don't try to skimp on the skimmer. You usually get what you pay for.

Get Aquarium Plants or Macro Algae

Freshwater aquarium keepers can use aquarium plants to compete for nitrates and phosphates. Saltwater aquariums can use a macro algae such as chaetomorpha. The plants or macro algae will consume nitrates and phosphates and compete with the undesirable algae forms.

Saltwater Aquarium Keepers - Use Biopellets

One of the more recent developments in the saltwater aquarium world are biopellets. These are tiny bio-degradable polymer based pellets that consume nitrate and phosphates as they break down or dissolve. You run these in a reactor chamber where you want to keep them tumbling. The output from the reactor is directed into or near your protein skimmer so the skimmer can remove the effluent from the biopellets. After running these biopellets for nearly a year now I can vouch that they work very well. The philosophy behind them is similar to carbon dosing but pellets are much easier to use in that you don't have to dose anything. You just replace the pellets as they dissolve, which can take several months before you have to replace them. They break down very slowly. I was extremely skeptical of these biopellets until I tried them for myself, but they do work.

Clean that filter

Hang on power filters and canister filters can do a fantastic job keeping your tank water appear clean and polished. But if you don't routinely clean out and rinse your aquarium filter media you are just providing foods for it to grow out of control. As the trapped particles in the mechanical filter mineralize (i.e. breakdown, decompose) they are providing energy sources for the algae. If you don't clean out your filter on a regular basis it could become a nitrate factory.

Vacuum the substrate and perform partial water changes

One of the coolest and most useful aquarium products is the Python Aquarium Vacuum. This piece of equipment hooks up to a faucet and lets you easily vacuum the tank with the waste water going down the drain instead of having to haul buckets around. To refill freshwater tanks you can reverse the flow and add fresh water back into the tank. Add the proper amount of dechlorinator into the clean water flow as it goes back into the tank. This is assuming that your tap water is good to go as far as nitrates and phosphates are concerned.

Saltwater keepers can use this tool too even though you should be using premade saltwater for water changes. For saltwater aquariums you will only be able to use the tank water removal part on this type of vacuum. You will still have to use that 5 gallon bucket or whatever you use to pre-mix the saltwater.

Scrub down the glass and then do a water change right afterwards. Vacuum the gravel or top layers of the sand to remove any detritus. If you have a saltwater tank and you have a bubble algae problem, now is a good time to carefully pull them from the rock work. Create a set schedule, say once a week and then stick to it. You really will enjoy your tank much more when it looks clean. The day after a water change and tank cleaning is a great time to take pictures too.

Get a refugium

A refugium can be a great place to keep competing macro algae or plants. Although primarily saltwater hobbyists utilize refugiums there really is no reason why freshwater hobbyists couldn't use a refugium setup as well. You can go cheap here too. Form a simple aquaclear hang on power filter, to a bucket, to a plastic tote, all make decent refugiums as long as you can easily hook them up to your display tank. Saltwater aquarium keepers often use fast growing chaetomorpha in the refugium to help compete against algae growing in the main tank. Once the chaeto reaches a large size you can prune some of it thereby exporting nutrients from the system. Freshwater aquarium keepers could use fast growing plants to provide a similar service. The plants and macro algae will compete with any algae trying to grow in the main tank and make it harder for algae to grow.

Replace your aging lights

Has it been awhile since you've replaced your fluorescents or metal halide aquarium lighting? As bulbs age they can emit a very different color temperature, frequently emitting light in the spectrum that many species of algae favor. Replace your bulbs every year or so can be a good guideline or even better, follow the manufacturer's recommended replacement schedule.

Ultraviolet (UV) Sterilizer

Some use a sterilizer to fight disease outbreaks in their tanks but they are even better at destroying algae. There are hang on the tank models that are really easy to install too. Get a power head for pumping water into and through the unit and that's it, you're in the business of uv sterilization. Sounds far out doesn't it? Pond keepers may be familiar with the pond UV Sterilizers. These sterilizers are on the expensive side but if you have really expensive fish or corals in your tank they may be worth researching. Also, like all aquarium products, some are better than others. More info on aquarium uv sterilizer.

Aquarium Blackout

Hobbyists will sometimes run their tanks with no lights for several days to combat algae problems. This is sometimes referred to as a tank blackout. Obviously, if you have photosynthetic plants, corals or inverts (clams) you don't want to try this. Cyanobacteria, often called red slime algae, is a problem often found in marine tanks. This stuff is a mess and can cause many a headache. Hobbyists will try anything to get rid of this unsightly bacteria that can quickly cover large parts of the tank. Doing a partial water change and vacuuming out as much of the cyanobacteria as possible and then doing a tank blackout for several days may work. But why did the red slime take hold in the first place? Lack of flow, no protein skimmer, overfeeding, overstocked tank, etc. are the usual culprits. Fix these and then see if the problem clears up before performing a tank blackout.

Algaecides, supplements and other products

There are many different products available that will make quick work of ridding the fish tank of algae. These are usually just short term fixes though. If you don't fix the original problem you will be spending a lot of money on these products. Use them with extreme caution, if at all. For example, many hobbyists on forums all over the net talk about some of the red slime removers and getting no adverse effects from using them. Indeed, they usually clear up the slime algae over a period of days. But, some of these products could potentially wreak havoc with the bio-filtration in the tank so research them thoroughly before trying them. I'm not saying that they will destroy your bio-filter, just that the hobbyists needs to be doing the legwork on any products and/or supplements they use on their tanks. The main thing to keep in mind though is did you fix the original problems causing the algae growth? If not, it will come back eventually.

There are also tons of supplements, vitamins and cure-alls available to hobbyists too. Are they really worth it? That is for you to decide, but be cautious about adding anything to your tank that you can't test the side effects of using. For example, do you have a strontium or molybdenum test kit? Neither do I and that is why I don't use those supplements in my saltwater aquariums, relying instead on regular partial water changes to replenish these trace elements. Some of these products are useful (buffer, calcium additives, plant foods, etc) but be a smart consumer and research these products before using them in your tanks.

To sum up: under stock, feed appropriately, use purified water when your tap water is suspect, perform regular partial water changes, maintain the filter and vacuum that substrate to help limit the amount of foods available. Keep your water parameters in line with what you are keeping too. For example, saltwater aquarium keepers should try to keep pH in a range of 8.2 - 8.5, sg at around 1.024 - 1.025, calcium at around 420 ppm and alkalinity at around 2.5 meq/L. If you still have a problem with algae growth test the nitrate and phosphate levels. Figure out why these levels are elevated and then fix them. Even after doing all of the above you will still have algae growth in your tank, but it should be much less than before and more easily maintained.

Thanks for reading.

Aquarium Algae Comments

From: Diane

I have two large goldfish in a 30 gallon with some anacharis and ramshorn snails. First, let me say that no one at the pet store will give me the straight scoop on how to balance my aquarium because then I wouldn't need to buy very much, so thanks for all of this very helpful info.

I thought the snails would help keep the algae down, but they really don't put a dent in it. I enjoy watching the snails, anyway, and my fish love to eat the baby snails, so it decreases the amount of fish food needed. I hoped the anacharis would help diminish the nitrates, so in reading about how to care for the plants, I learned that, while they use carbon dioxide during the day when the light is on, at night they use oxygen. So, I started changing the way that I aerate depending on whether the light is on or not. When the light is on, I fill the aquarium to the bottom of the pump outlet, so there is little surface agitation. This helps to preserve enough carbon dioxide for the plants. Then, at night, I reduce the water level by about an inch. This causes a lot of surface agitation. I also move the pump intake close to the bubble stone bubbles, but not directly in the stream of bubbles. The pump catches a few bubbles and blows them through the filter, making a cloud of much tinier bubbles. It makes the aquarium water look like champagne and it's very beautiful. The next morning, THE ALGAE IS MOSTLY ALL GONE. Don't know why! Also, the aquarium smells much better, since the odor seems to caused by the algae. I move the intake away from the bubbles, raise the water level, and turn on the light. The anacharis goes to town, and the aquarium is clear as a bell.

I reactivate my carbon by first boiling it, and then baking it at 200 to 250 degrees until it is way past dry. Then I soak it in aquarium water before I put it back in the filter. It works great! I tried this after learning thatwait long enough. In the summer, just leave it in the sun for a couple of days. I change it almost every day. You can't imagine how much waste these goldfish produce. I use the Fluvial carbon sachets so I can just change the carbon without changing the whole filter cartridge. I put the cartridge and the sachet in a knee-high stocking.

I rinse the cartridge in aquarium water everyday, and I scrub out the inside of the pump every few days because algae builds up on the inside surfaces and fuels the algae in the tank. I don't know nearly as much about what I'm doing as you all, so let me know what you think about my comments. Thanks again.

Thanks for your comments. I'm not sure you could ever have a "balanced" goldfish tank since you still have to do water changes on a regular basis because they are large waste producers... I've heard of others reactivating activated carbon but it sounds like a lot of work/time since it's still relatively inexpensive to buy new AC.

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