Combating Green Algae to Get Rid of Pea Soup

Green water can be controlled rather easily.

Green water algae can be a big problem for the aesthetics of your aquarium. No one wants a planted tank, or any tank really, with water that looks like pea soup. It seems to come up quickly but luckily there are a few things you can do to combat it to get your tank back to looking great.  While green water algae can be unsightly it isn’t necessarily dangerous to your fish.  Some fish live naturally in water filled with green water algae.  We just don’t want to keep them in such conditions that we can’t see them.

There are many different kinds of algae that can grow in your tank.  This particular algae we are talking about today hangs in the water column.  It doesn’t cling to the glass and other flat surfaces.  To be absolutely certain you can take a water sample.  If it’s clear you have another algae type, but if the water is green then you have green water algae.

Sometimes it will disappear on its own as the tank balances. This is most common in a newly set-up tank or when adding a larger bioload like more fish. As you add more fish you also add more food and waste to the water column. Since there is a new abundance of nutrients algae proliferates quickly. In some cases, your bio-filter will ramp up production until it balances out and defeats the algae bloom. However, in many or most cases you have to remedy the cause. If you don’t remedy the cause it will come back when you have stopped fighting it.

If you messed up and added way too much food one day, or found a dead fish that was decomposing and got green algae, you can remedy the problem and it should go away. In the meantime, you can reduce your lighting to around 5 hours a day until the tank clears up. In the event that you overfed or found a dead fish in the tank a water change and gravel vacuuming should be in order in addition to lowering your photoperiod time.

Green water algae can be cleared rather easily.If you have a really bad case of green algae and have been fighting it you may have to resort to more extreme measures. A total blackout for 5 days can help kill the algae but it still won’t remedy what caused it. Diatom filtration or a UV sterilizer will also get rid of the green algae but it will not stop what is causing it. This is especially notable for repeated cases of green algae.

Something has caused enough nutrients in the water column for an algae bloom. In a newly set-up tank, this is more common as the biofiltration has not caught up to the bioload and excess nutrients (ammonia) are quickly utilized by algae. In older established tanks algae blooms like this means that there is a new source of nutrients or an excess of light for algae to use. Either remove what is causing the nutrient excess and stop what’s causing the problem or you will be combating the symptoms indefinitely.

Limiting your lighting and nutrients are the biggest tools against all algae. It may sound counter-intuitive but plants are a good tool to combat algae by fertilizing them. Healthy growing plants use nutrients. Fertilizing your plants more can help them out-compete algae for the nutrients that algae need. In order to do this, you have to have healthy plants and a fertilizing schedule.

Overall green water algae is mostly unsightly and not difficult to get rid of.  Providing proper lighting periods and a balanced tank can do a lot towards getting your water clarity up to par.  It’s not hard to do and isn’t overly complicated.  Control the lighting and do something about excess nutrients by helping your plants outcompete the algae.


by Edward Johnson
Photo by Ivan Bandura
Photo by Ron Greene

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