As we've said elsewhere, the easiest way to avoid green water is to set up your pond correctly from the start. To see what we mean by that, read this article. If you are well-beyond the initial set up, read below for some tips on what you can do today to clarify the water in your pond.
Before we begin making adjustments to our pond, we must first determine the cause of the green water. It could either be single-celled algae, or it could be tiny particulates (dead string/carpet algae) suspended in the water.
(This part is very important) Take a sample of the pond water in a clear container and place it against a white background:
- Do you see bunch of little particles and bits of stuff in otherwise fairly colorless water? If so, then you don’t have a planktonic algae problem, and you’ll just need to remove the suspended debris from your water through filtration or cleaning. (A fine filter pad inserted in your skimmer between the basket and the pump will catch those finer particles that slip thru the net. The pad will need to be hosed clean every hour or two to over the course of the day; it tends to load up rather quickly in poor water conditions. These pads can be folded in half to double the efficacy, and you can reuse the same pad until it starts to fall apart. When used in combination with flocculant or S.A.B. this method should make a healthy difference in a day or two.)
- Does the water appear green like kiwi juice? If so, then you have planktonic algae, a microscopic, single-celled plant that is too fine to be filtered out like those larger bits that can be seen with the naked eye. In that case, the rest of this article was written just for you!
Planktonic algae is a simple organism, and is most happy when it gets a lot of sunlight. This is why you can have clear water all winter, and then when the weather warms up your pond suddenly looks like a lifetime supply of pistachio milk! It’s not a sudden infestation, the algae was already there in a state of dormancy. It was merely waiting for the right conditions to start reproducing, and when those conditions arrive, it gets busy, and fast!
1. Food: Nature doesn’t like anything going to waste; where there is abundant food available, something will eventually come around for the feast. Like any organism, algae needs to feed, and a bloom of the pea-soup type means there is an imbalance in your water that nature is correcting on her own. This imbalance is typically an excess of micronutrients in the water. The most common cause for this excess is an over-abundance of fish food. Koi and goldfish will naturally forage for their food, and they can get by on their own without us supplementing their diet. Although we do love when our koi greet us at the edge of the pond and take food right out of our hands, we are careful to give them only premium fish food that contains quality food-grade proteins and omits cheaper ingredients like bulking agents and binders. Premium food can be more thoroughly digested by the fish, thus it contributes less waste to your water. So if you have green water, try taking a break from feeding your fish, or at least reduce the feedings to once a day, limited to what they will consume within five minutes, and be sure you are providing a high-quality food. Even if your fish appear to be asking you for rations, they’ll be fine on their own.
2. Biological Filtration: Biological filtration is simply employing helpful strains of bacteria to consume the nutrients that would otherwise accumulate and fuel algae blooms. We use a handy component called an Autodoser that provides a steady stream of specially-formulated all-natural water treatments. For regular maintenance we use Autodoser-Maintain to keep our ponds balanced and clear. It makes a big difference. This stuff contains the same beneficial bacteria in our powder or liquid, plus enzymes and a powerful phosphate binder to keep water clear and healthy. If you are already doing this and experience a spike in algae, such as occurs after a storm or disruption to your pond, you can double the dosage for a couple days. We use our Autodoser all season, even when the water is already clear. It’s a proactive way to maintain the water quality we want. It combats algae by starving it of the nutrients it uses to grow. This works best when used alongside a mechanical skimmer and a biological filter such as a BioFalls.
3. Aeration: Keeping your pond well-oxygenated is a key element of a healthy pond. While bacteria does most of the work, it needs plenty of oxygen to keep it functioning at peak efficiency. A waterfall is an excellent way to introduce oxygen into your pond, but if the pond is larger than 10‘ then the oxygen supplied by the waterfall may not reach to every corner. Adding a fountain or aerator to any stagnant areas of the pond will keep those areas well-supplied with oxygen and combat the algae that would otherwise flourish.
4. Plants: A pond is not complete without aquatic plants, and they do more than just look good. The right plants will compliment your beneficial bacteria by utilizing nutrients in the water, serving to starve out algae. The best plant for this is thalia. It grows large and fast, and consumes a lot of the nutrients that would otherwise become food for algae. Floating plants like water lettuce or water hyacinth are also helpful; not only will they use up extra nutrients, they will also help block some of the sunlight that fuels algae blooms. Water lilies, while excellent at shading your pond, are comparatively poor at using up nutrients. So if you only have lilies, you may want to consider adding something with a bigger appetite.
5. Sunlight: We just covered how floating plants and water lilies can help reduce algae by providing shade. This is an easy change to make that can have a dramatic impact, and much easier than planting a tree for the same effect. It is not always feasible to locate the pond near a large shade tree, and when adding one near your pond you have to be mindful of growing roots disrupting the liner. Some trees, like willows, are notorious for having roots that can bore thru and destroy a pond liner. Another drawback of relying on trees for shading your pond is that they will certainly introduce more organic debris into the water, which has a negative impact on water clarity.
6. Bacteria: Yes, it was just mentioned in #2 under biological filtration how beneficial bacteria is the foremost defense against pea-soup pond water. What we did not discuss is how to support the bacteria that is already present. You don’t have to do anything special for bacteria, it will do fine without any interference. In fact, your interference is the one thing that is most likely to inhibit it from working! How might you interfere with bacteria? By simply cleaning it off your rocks, and most importantly, your filter media. Those little balls in the mesh bags inside of your BioFalls are designed to provide maximum surface area for the bacteria to colonize. It is only necessary to rinse your filter pads and the bioballs or lava rock in the spring and fall, or when the filter is literally clogged and the water flowing through slows down. It is preferable to use pond water to perform this task, as the risk of sterilizing your biological system is greater when using municipal tap water.
7. Rocks & Gravel: Rocks are a hallmark of the ecosystem pond, and they serve several important functions. They protect the liner from UV damage, they create habitat for invertebrates and frogs, they enhance the natural appearance of the pond, they allow your fish to forage along the bottom as they would in nature, and most importantly, they provide lots of surface area for that helpful bacteria to colonize, significantly increasing the biological filtration capacity of your pond. We recommend a ~1.5“ layer of 3/4" to 1.5" rounded river gravel. This gravel bottom will cultivate a coating of green carpet algae, and that’s not a bad thing. The carpet algae will help rinse the water and keep it clear.
8. Cleaning: Annual cleaning of the sludge and muck that accumulates on the bottom of the pond is an important part of maintaining clear water. That muck is like compost, and as you might imagine, it is full of plant-fueling nutrients. Removing it in the spring and/or fall is the best way to keep it from fueling algae growth during the summer. To compliment these deep-cleans, it is wise to remove any debris that lands in your pond as the season progresses. Those little maintenance tasks can make a big difference to the overall water quality.
9. Water Treatment: As animal lovers, we are very much biased towards using natural, non-toxic treatments, and we strongly discourage the use of any algaecides. The problem with chemical algaecides is they wipe out the algae all at once, leaving the pond filled with decaying algae that just fuels the next bloom. If being trapped in an endless cycle of bloom-bust isn’t bad enough, a nasty side-effect of all that algae decomposing at once is it uses up all the available oxygen, leaving your fish gasping at the gills and possibly even killing them. It happens far too often, and once the fish start showing signs of a problem it becomes a much more expensive problem to fix, if they can even be saved at all. This unfortunate scenario is entirely preventable, if only algaecide manufacturers would educate their customers about the risks of using their product.
10. Establish Harmony: A common mistake people make when trying to achieve clarity is to simply drain all the green water and replace with fresh water from the hose. This may give immediate results, but they are not lasting. The same things that caused the water to turn green in the first place will happen all over again, delaying the attainment of a balanced ecosystem, plus the sudden change in water chemistry brings the risk of shocking your fish. A far more preferable option is to let the pond get established and to allow all the cooperating elements of the ecosystem to mature; this increases the pond’s tolerance to changes, whether they be environmental or deliberate. The only time we typically replace water is during cleanouts, when it is normal to replace up to 50% of the water as part of the overall refresh, accompanied by treatment for chloramine and water testing to ensure the parameters stay within the ideal range for that pond.
These ten steps can save you hours of guesswork and frustration, please share them with any fellow pond owners you know who may be struggling with green water. It is not something that will go away immediately, and that leaves many people to escalate their treatments, further compounding the problem. After reading this article, you have hopefully gained an understanding of green water, plus the knowledge of how to clear it up and prevent it from developing. By following our advice, we hope you can enjoy your fish for many more years, and will have the insight to make knowledgeable decisions when comes to the management and care of your pond.