905-715-2447 Spring Hours: Tuesday to Sunday 10:00 am-5:00 pm 3301 Sideroad 10, Bradford, ON Canada
905-715-2447 Spring Hours: Tuesday to Sunday 10:00 am-5:00 pm 3301 Sideroad 10, Bradford, ON Canada

How To Eliminate Green Pond Water

Hydrosphere Water Gardens > Pond Advice & Tips > How To Eliminate Green Pond Water

How to Clear Green Pond Water (Algae)

Green pond water is caused by single celled, free floating algae, also known as planktonic algae. It is one of the most common problems that people have in their ponds and can sometimes be very difficult to control. There are several ways to naturally control control algae and clear green pond water. Follow the steps below to clear your pond naturally and you will achieve a more balanced ecosystem, with longer lasting results.

However, some ponds seem to turn green year after year, even though all the usual criteria for maintaining clear water are met. This could be from a number of things, such as a build up of organic matter in the pond, a heavy fish load or even your water source. Other ponds just need need a ‘fix’ at certain times of the year, often during the spring or early summer. Either way, we have the solutions to kill algae and clear green pond water.  

For more information on algae including string algae see our Algae Control In Ponds page.  

What Causes Green Pond Water?

The algae that causes green pond water grows because there is a nutrient imbalance in the pond. When nitrates and phosphate levels in the water are high, an algae bloom usually follows. There are several reason why nitrates and phosphate levels become elevated in the first place. One culprit is sludge and muck on the bottom of the pond. As this layer of organic matter (dead algae, fish waste,  leaves, grass clippings etc ) decomposes, it releases nutrients into the water which provides food for algae to grow. As more muck builds up, it releases more nutrients.

Another very common cause of algae is having too many fish in the pond. Keeping koi or goldfish in a pond is very enjoyable, but the waste that fish produce gets broken down into nitrates which feeds algae. Most people buy koi when they are small, not realising how large they can grow. 4 or 5 large koi can produce a substantial amount of waste, causing an nutrient imbalance in a small pond. Goldfish, on the other hand, don’t grow very large, but they are very prolific and can spawn several times a year. People that add a few goldfish to their pond are often overrun with several generations of goldfish in just one  two seasons.      

The last cause of green water we’ll deal with is plants, more precisely, the lack of enough plants. Pond plants naturally compete with algae because they consume the same food – nitrates and phosphate. If you don’t have any plants in your pond, you will be guaranteed to have an abundance of algae because there is nothing else to lower the nutrient load.

Clear Your Green Water Naturally

Step 1 – Clean  Your Pond & Reduce Sludge  

the amount of nutrients that feed algae can be significantly reduced by cleaning the muck and sludge from the bottom of your pond. In small ponds, this can easily be done with a long handled net. If you have a larger pond, you will find a Pond Vacuum to be a very effective and easy way to remove sludge. It is usually sufficient to do this a few time a season, in the spring, mid summer and again in the fall after the leaves have fallen from the trees. Using a net to cover the pond in the fall will prevent leaves from getting into the pond in the first place, making maintenance easier. Another way to reduce the organic matter is to add a Sludge & Muck Reducer to the pond. These muck reducers are made up of all natural, beneficial bacteria and enzymes that consume the sludge and convert it into a nitrogen gas that simply ‘bubbles’ out of the pond. CrystalClear® MuckOff™ is a an excellent product that reduces sludge very effectively.

Pond enthusiasts with larger ponds often add a Pond Skimmer. Skimmers help to reduce the need to clean the bottom of your pond as often because they continually skim the surface of the pond, preventing leaves and debris from sinking to the bottom. It also makes filter and pump maintenance mush easier. Bottom drains are also becoming more common in ponds because they continually pull waste from the bottom of the pond and put it into the filtration system where it can be easily removed. Bottom drains practically eliminate the need to manually clean or vacuum the bottom of your pond. 

A fairly new product that naturally clears ponds is Nualgi. Nualgi is not an algaecide, once added to the pond it creates a bloom of Diatom algae (the good kind!). The diatom algae bloom out-competes nuisance algae for CO2, Nitrates, Phosphates and other nutrients, causing the bad algae to die off. We have had good results with it here.

Step 2 – Reduce Fish Load

As we already mentioned, fish are a major source of the nutrients that feed algae. If you are having reoccurring or constant algae problems, it might be time to reduce the number of fish in your pond. It can be difficult to part with koi or goldfish that you have had for a long time, but if you have too many fish, this can also cause problems with water quality which leads to sick fish or even sudden die-offs after spawning or during winter.

Give a few fish away to friends or neighbours with ponds. Sell or give away your fish by placing an ad on a local newspaper or online.

Once you have reduced the number of fish, try to resist the urge to buy more. If you have only goldfish in your pond, try feeding them less food. In most ponds, there is an an abundance of natural food such as algae, worms and insect larvae that goldfish can feed on. By feeding your goldfish less food, they will still be healthy, but they will produce fewer babies.

Step 3  – Add More Plants

Not only do plants directly compete with algae for the nutrients in your pond, they also shade the pond, provide shelter for fish and help to create a more natural environment. The more plants you have the better, however some plants are more effective at reducing nutrients. we call these plants Clear Water Plants. To find out more information, visit our Clear Water Pond Plants page.

Other Algae Treatments

If you have tried almost everything and still have a green pond, don’t fear, there are still other solutions available. First, if you don’t want to use chemicals, but want guaranteed results, install an Ultraviolet Clarifier. Ultraviolet (UV) clarifiers work by using ultraviolet light to kill free floating algae. We carry many sizes of UV Clarifiers that will suit your pond.  If all else fails, these are sure to work. If you purchase a UV light that is correctly matched to the size of your pond and have the correct water flow passing through it, you will have clear water within two weeks. Guaranteed!

ProFix (formerly D-Solv 9 is an algaecide that not only clears green pond water, but it also eliminates string algae. D-Solv 9 is very concentrated, a 16 oz bottle will treat 9600 gallons of water. If you have a large pond, a 1 gallon bottle is also available that treats 76,800 gallons! It sometimes works with just one treatment, but sometimes take 2 to 4 treatments depending on the conditions in the pond.