Dealing With Algae 101

At some point just after your tank has completed its cycling most novice will encounter outbreak of algae. At this point in time, the outbreak of algae will almost certainly determine the outcome of your hobby – to give up or to pursue.

So What Went Wrong?

In the world of high tech planted tanks there are a lot of variables that you need to juggle with. Any one of these parameters moving out of the threshold will trigger algae outbreaks.

I came across forum posts whereby Reef tank veteran found striking a balance in planted tank more challenging than a reef tank.

The below factors can trigger algae:

  • Inconsistent CO2 supply ?
  • Not enough CO2 supply ?
  • Too much lights ?
  • Lights too low ?
  • Too much ferts ?
  • Too little ferts ?
  • Not enough water flow ?
  • Too much water flow ?
  • Too much gunk/waste ?

In nature there are triggers hardwired into every thing. When plants deteriorate it is one of the triggers in nature for algae to spawn. If your tank is full of healthy aggressive growing plants you will almost never find algae, because there is no trigger.

Stainless Steel Algae Scrapper

AliExpress is selling it for $12 and provides free shipping!!?!

Algae Combat – Immediate Remedy

There are a lot of recommendations online, some conflicting, mostly hard to implement without having a master test kit.

From my experience, the immediate step to take is to reduce lighting intensity and photo period. This always works. But this is a short term remedy.

Long Term Strategy

Your long term remedy or should I say goal is to establish a balance between nutrients and lightings (and CO2). When you have a balance tank your tank will be almost maintenance free! I spend more time viewing the tank than scraping algae.

For reference, I only need to perform water changes weekly, trimming every month, and canister cleaning every two months. Very minimal algae scraping.

First Step

I assume you have taken the step to reduce lighting and photo period.

  1. Reduce light period/intensity
  2. Scrape off the algae.
  3. Continue ferts regime. (If using EI reduce the half the dose).
  4. Continue CO2 injection rate if any.
  5. Observe the rate of algae growth for two weeks.

Try to achieve a balance tank with low light settings.

If you cannot achieve a balance tank with low light settings, reduce your fertilising regime further or change to a new fertilising regime altogether. Or continue to reduce lighting.

If your light is dimmable, I will recommend using 40% of the full intensity of your lighting. If your light cannot be dimmed, try raising it higher. You can raise your light’s height with a light stand or acrylic brackets.

If you do not have CO2 injection, unfortunately, you will not be able to increase the lighting intensity beyond the reduced lighting setting because the limiting factor here is CO2 present in the water. Without artificially injecting more CO2 into the water I am afraid you are stuck with the current growth rate and brightness.

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I know a lot of hobbyists are reluctant to go into high-tech way due to the myth they read in online forums of high-tech means high investment. Or they are simply too afraid of failure. I have some guides here to help hobbyists access to CO2 injection at a fraction of the costs.

Second Step

After achieving a balance tank with a low light setting, it means that the light strength is matched with the nutrients (and CO2). They are in equilibrium.

However, you may find that with such low lighting the tank is not appealing. It is unlike those you see in photos.

Well, to increase the lighting intensity means your plant will be given more energy for photosynthesis. The rate of growth will also increase as a result, provided all the plant’s needs are met.

The key here is all plant’s needs are met.

With a higher intensity light, you need to feed your plant more nutrients. But exactly how much? Unless your plants speaks to you directly, otherwise how are you supposed to know what your plants need, and at what quantity?

This question has troubled hobbyist from the beginning. And so Tom Barr derived the E.I. (Estimative Index) method of fertiliser dosing.

In short, this method simply adds excessive fertilisers to your tank, so much so that there is no way macro or micro deficiency can take place. In this way, you can eliminate nutrient deficiency from the equation, leaving you with light intensity and CO2.

Light intensity is the easiest to control. So that leaves just CO2 as the last variable. And so, hobbyist will just blast their CO2 in similar E.I. way. Level so high that any more it will kill your fishes.

Now back to the question, you have reduced your light intensity for a few weeks now in order to combat algae. And you have successfully achieve a balanced tank with no much algae. But you want to increase the intensity for your tank now looks kinda dark and sad.

Now you want to increase your lighting intensity.

  1. The first thing you should increase is CO2. Increase your injection rate two fold as long as oit is within the tolerable limits.
  2. Increase your lighting intensity by another 20%
  3. Don’t increase your ferts doses just yet. (If you change too many variables concurrently you may throw your tank off balance immediately. Furthermore you will not be able to determine exactly what causes the problem.)
  4. Observe for two weeks.
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With higher light intensity and higher CO2 injection rate, plant growth will be accelerated and you can tell the growth rate visually.

After which should you then try to adjust your ferts doing. The moment you realise there are signs of algae growth reduce your dosing. Wait. Observe.

Remember, the effects of changes to your action takes weeks to become visible, not hours or a couple of days.

My rules is always

CO2 > Lights > Ferts

Quick Fix

If you cannot be bothered to go the proper way, then there are a few weapons in the arsenal that you can deal with algae.

Blackout Method

Blue Green Algae BGA treatment

The blackout method involves denying algae (and your plants) the food of life – Light.

Algae are simple organism and they do not have much food reserve as compared to plants. When denied light for a few days, the algae will be starved to oblivion before your plant.

Depending on the type of algae you are dealing with, blackout period range from three days to 5 days. The longer the blackout the higher the collateral damage to your plant.

How to:

  1. Feed your fishes as much as possible. For during the next few days you will not be able to feed them.
  2. Perform a partial water change.
  3. If you do not have an air stone you will need one as the plant will not be able to photosynthesise to produce oxygen.
  4. Use any materials that can prevent lights from reaching inside the tank. I use black trash bags.
  5. Tape the tank up completely.
  6. Decide on how many days to blackout.
  7. On the last day of your blackout period, wait until night falls before ending the blackout treatment. Make sure you use a light far away from the tank. After many days without lights your fish will be uncomfortable with lights. I do not recommend switching on lights to inspect the algae. I would wait until next day.

Nevertheless, you only treated the symptoms of your problems. The fundamental problems are still not address and algae will return eventually.


Nuke or chemical warfare. There are Seachem Flourish Excel, H2O2, and other commercial algae removal chemical.

Seachem Flourish Excel

Seachem Flourish Excel is a form of liquid carbon supplement for plants. Back in December of 2004, someone posted in the Aquatic Plant Central forum that due to an accident he dosed no less than 5 times the amount of this liquid into his tank. A couple of days later, all the algae was gone!

Soon people started experimenting with various amount of doses. And the general consensus is that an amount of 2.5x to 4 times the daily recommended dose is safe to be used to control algae.

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However, my personal experience was that shrimps somehow are affected by high level of Flourish Excel. They will become less active and just stayed in a location to brave out the Excel nuke.

Again, you are not addressing the source of the problem but treating the symptoms.


H202 is Hydrogen Peroxide.

Its name may sounds dangerous but it is actually a very safe solution to use in aquarium. Hydrogen Peroxide when comes into contact with your aquarium will begin to break down into water and oxygen, nothing else.

In nature when sunlight reacts with water surface H202 is created in small amount as well. Hydrogen Peroxide has antiseptic properties and are commonly used as an antiseptic. As such you can find Hydrogen Peroxide in almost any pharmacies. And it is cheap!

Dosing Instruction

1ml H2O2 per 2 gallon, or 0.5ml per gallon.


Switch off all water pumper, power heads and filters 15 minutes prior to administering. This is IMPORTANT. What we are trying to achieve here is absolute stillness in water.

Next, use the formula of 1ml of H2O2 per 2 gallon as your guide. Extract the H2O2 using a syringe. Reach down to the area affected most by the BGA REALLY SLOW, making as little wake in the water as possible.

Squirt the H2O2 in short burst DIRECTLY onto the affected area. FIRE IN THE HOLE! Immediately you should see that micro bubbles forming on the algae. If the water is extremely still the entire are where you have squirted the H2O2 will begin to have chemical reaction.

Visually you should be able to see the affected area melt away. And within seconds, some how, the shrimps are all heading this way to feast on the algae.

Once your squirting is done, just go fix yourself a cup of coffee and watch the bubbles. After 5 minutes or so when the bubbles stopped, it is time to perform your water change. Do not repeat this treatment until next week on your water change day again.

Repeat weekly treatment until all algae are gone. You will also notice that areas not squirted by the H2O2 will see algae dying off or retreating. Therefore it is not necessary to squirt H2O2 directly onto affected areas, just those heavily infected area.

If you are dealing with the mother of all aglae – the Blue Green Algae, H2O2 is the ultimate trump card against BGA.