Posted by Bali Reef Aquarium on

There's nothing more frustrating than a green pond right?
Your koi fish looks healthy and fine, but your pond is green! How frustrating!

The green pond is usually caused by Phytoplankton-- microorganisms that belong to the family of green algae. Generally, a green pond is caused by two types of algae. The first type is the fibrous algae, they stick to the side of the pond. The 2nd type is called One-celled Algae, they float around the water--making the water appear green).

So, what causes the algae bloom inside the pond?

1. The Location of The Pond

The location of the pond which is directly exposed to sunlight accelerates the process of photosynthesis of algae in the water. In addition, algae easily absorb oxygen, food, and nutrients in the water thus speeding up the reproduction process. Therefore, the indoor pond has a lower risk than an outdoor pond because it is less exposed to sunlight.

To minimize this problem, we suggest you provide shades, such as lush trees beside your pond or lotus plants on your pond.

2. Poor Pond Filtration System

You have added sponge, bio ball, and foam but why does it still look green?

In a pond filtration system, the placement and selection of the filter media is the most important thing of your successful filtration.

Here is an example of the complete and correct filtration media arrangement. It is initiated by incoming water flow that will lead to;

A. Skimmer

The skimmer is a mechanical filtration system that works by collecting wastes such as leaves, grass, and small twigs that fall on the surface of the pond. The skimmer will draw the water on the surface and then filter the wastes which after that will send the filtrated water to the pump.

The skimmer also serves to keep water from dissolved organic compounds. Without skimmers, it's possible that the surface of your pool will be covered by an oliy thin layer(i.e protein bio film). This layer will inhibit the exchange of oxygen absorbed into the water.

B. Mechanical filter

Mechanical filters serve to filter solid dirt (e.g rotten plants, insects, dried leaves, etc.) and liquid dirt (fish droppings, mud, etc.) in ponds. Due to the different forms of impurities, the preparation of mechanical filters starts with materials that have large pores and then followed by the filters with thinner pores. For example;

Blue Bio Matt->Black Bio Foam->White Sponge->Brush

C. Biological Filter

Biological filters work with good bacterias that decompose ammonia (i.e Nitrosomonas sp, and Nitrobacter sp.). The good bacteria live and reproduce inside the pores of the biological filters with a supportive biological environment. Nitrosomonas will convert ammonia into nitrite, while Nitrobacter will convert nitrite into nitrate. Biological filters will reduce ammonia produced by fish, fungi, and fish food residue in the water.

The production of ammonia will be increased if we overfeed the fish. It will harden the work of the decomposing bacteria in the filter.
Use the right amount of biological filter in accordance with the number of fishes inside your pond.

These are some examples of a biological filter. You can use;

1. Bioballs

2. Ceramic Ring(Bio Ring)

3. Kaldness

4. Super Bio

D. Chemical Filter

Chemical filters are filters that bind harmful substances left in the water, ensuring that no more toxic substances are present. Chemical filters work by binding / absorbing chemical substances, it is necessary to change filters periodically when the filter media is saturated.

Here are some types of chemical filter media:

1. Zeolite

It is a grayish natural stone fragment containing hydrated alumino-silicate with cations of sodium, potassium, and barium. This will help bind the remaining ammonia in the water, therefore the zeolite will be saturated after 6 months of use and the stone must be replaced.

2. Activated Carbon


Activated carbon is used to absorb unwanted organic substances, such as phenols, detergents, cresols, as well as toxic substances that cannot be deciphered. This activated carbon is also able to purify water and deodorize the pond due to its neutralizing properties.

It should be noted that the filtering ability of activated carbon will decrease (saturate) over time. Therefore, there must be a periodic replacement every 4 months. Activated carbon also must be washed clean before being put in a cloth net and placed in the chamber.


E. UV Lamp

The UV lamp is an additional filtration system that works by effectively killing bad bacterias, viruses, protozoa, algae, or fungi. Because of the strong radiation beams, it is capable of killing microorganisms contained in water.

In general, UV Lamp is placed on the last filtration chamber. The radiation beams from the UV bulb will weaken over time, therefore the UV bulbs should be replaced once a year. Lastly, please avoid looking at UV lights directly as it may cause harm to the eyes.

F. External Filter

Well, if you don't have time to make a chamber filter, an external filter can be an alternative! An external filter or what is commonly called a “Cannister Filter” is a practical bucket-shaped filter that is already filled with mechanical, biological, and chemical filters. In some brands, external filters are equipped with a UV filter and a pump inside. Even though it's practical and efficient, don't forget to do regular wash for filter media. For the Hozelock brand, they do have a backwash system, so we don't need to worry about that.

3. Rarely vacuuming and cleaning the pond

The nutrients that feed algae can be significantly reduced by cleaning the sludge and dirt from the bottom of the pond! For a small pond, it may be easy for you to clean it with a manual brush. But what if it is a big pond? it is extremely difficult!

Therefore, the pond vacuum tool is very helpful! Pond vacuum will help you pull in the dirt and sludge on the bottom of the pond more practical and lighter. You just need to vacuum the pond once a month and change the water by 25%.

When its time to change some of the media filters, its best to vacuum the bottom of your pond first. The new media filters will work effectively!

Or if you don't have enough time to deal with this, you can contact our project division here

4. Too Many Fish in The Pond

As we already know, fish foods and wastes are the main sources of nutrients that feed algae. If you have persistent algae problems, it may be time to reduce the number of fish in your pond. Maybe you will find it difficult to part with your favorite koi or goldfish that you have had for a long time, but if you have too many fish, it can also cause poor water quality that leads to sickness or even sudden death after the transition season.

You can give some of your fish to friends or neighbors who have a pond. Don't forget to resist the urge to buy more! Reducing the number of fish and feeding them sufficiently will have a significant impact on the pond!

5. The Lack of Plants in The Pond

Without plants, the algae will rampantly eat all the good nutrients in the water, thus accelerating their growth and reproduction. Therefore, by adding water plants with strong nutrient absorption on the edge of the pond, it will indirectly seize the nutrients needed by algae, thereby inhibiting their growth.

Aquatic plants also shade the pond, provide shady shelter for the fish, and help create a more natural and cool environment. With the right number and types of plants, the pond will be clean and the ecosystem is balanced.


Other Alternative Treatments

1. Use Algae-Killing Solution

Now, for prevention and practical solutions to get rid of algae in the pond, you can use an algae-killing solution that you can find at an aquatic store, called 'Never Green algae killer.' Besides inhibiting the growth of algae in the pond, this liquid is also able to eradicate bacteria, viruses, parasites, and fungi. And also eliminate the fishy smell in the pond.

2. Add Liquid Bacteria

Nitrosomonas and Nitrobacter bacteria can help decipher decomposed food and sludge at the bottom of the pond that used to be nutrient for algae. Therefore by adding bacteria, it can help to maximize the filtration process of your pond.

3. Clay Koi

Koi clay can help to control the growth of algae when added to your koi pond. It has been proven to be really effective in restraining and killing string algae. This clay is also a natural way to add a lot of beneficial minerals to your pond. It is a Calcium bentonite clay which when added to your pond will temporarily cloud up. It clears up during the day after adding lots of great minerals and removed toxins.
When Koi Clay is added to the pond, it’s negatively charged clay particles attract and bind the positively charged toxins and heavy metals in the water, much better than charcoal and other filter products, improving water quality and making the pond water healthier for fish and other pond inhabitants.

Well, it turns out we have a lot to do for a good quality filtration system! Of course, all the hard work will be paid off with satisfying results. Rather than creating a makeshift filtration system, it's better to renovate your filtration system from now on to make it easier for you to maintain in the future!

That's all from us, I hope this article is useful guys!

For our valued readers, are there any topics that we need to cover? Who knows we can help you. Let us know in the comment section. Have a good day!

Evelyn and Widya Here! This project is fully supported by Bali Reef Aquarium. If you like our article, kindly share this article to your friends and family that have similar problems. Thank you!

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