The first thing to understand is that it’s not really your water that is green … what you’re actually looking at is millions of single-cell algae swimming in the water. Algae by itself is not inherently bad. It’s only there because it’s nature’s way of dealing with excess nutrients. It usually won’t hurt your fish unless it grows to extreme volumes. Every pond can and should have at least a little algae in it- it is an ecosystem, after all, not a swimming pool. Pond owners outside the U.S. sometimes even embrace the natural beauty of an emerald-colored pond.
Most American pond owners, however, prefer the aesthetics of crystal-clear water so they can see and enjoy their beautiful fish. The bad news is there are many possible disruptions to your pond’s ecosystem that can tint that beautiful water an unsightly green or brown. The good news is you can keep your water clear relatively easily – and without using harsh chemicals.
At a Glance: How to Keep Pond Water Clear
- Understand that a little bit of algae or discoloration is normal
- Use beneficial bacteria to starve single-cell algae that turns water green
- Add a wide variety of aquatic plants to starve string algae
- Add a larger biofilter
- Don’t overfeed your fish
- Don’t overcrowd your fish
- Don’t power wash your rocks
- Keep your water oxygenated
- Watch for any debris that may be washing into your pond
1. Learn about your pond’s ecosystem
Your pond isn’t just a a beautiful relaxing place to hang out with friends. It’s a living, breathing ecosystem full of fish, plants, bacteria and other life that you probably can’t even see.
Educating yourself about how all of these elements interact can go a long way toward achieving the crystal-clear water you need.
So let’s start with a primer on how exactly algae ends up in your pond in the first place. Pond owners typically worry about two types of algae: the single-cell kind that turns your water green, and the stringy stuff that hangs off your rocks.
Single-cell algae lives off of the nitrites that build up in your pond when bacteria break down harmful ammonia. Other bacteria break down these nitrites into something called nitrates, which feed string algae.
Once algae sets up residence in your pond, you have two options: kill it with chemicals or starve it by removing the nitrites and nitrates. We’re going to go with Option B. Read on…
2. Add plenty of beneficial bacteria
Green water is single-cell algae consuming nitrites. Beneficial bacteria also consume nitrites. The secret to clear water, then, is to grow enough bacteria that all of the nitrites are consumed and none is left for single-cell algae – starving the algae so it doesn’t grow and make your water look green.
But isn’t bacteria bad?
No, not in this case. Beneficial bacteria is a product sold specifically for pond maintenance and is one of the safest and most natural helpers you can add to your pond water. You don’t have to worry about adding too much – unlike with algaecides, an overdose won’t kill your fish or plants – and it’s safe for pets and humans.
You can either add bacteria manually or buy an autodoser that will do it for you. Exact amounts will depend on the size of your pond and the specific product you choose (liquid, tablets. etc.). Just follow the directions on the back of the container.
3. Add a larger biofilter
Biofilters are a kind of party spot for those algae-starving bacteria. And anything that makes your bacteria happy will make your pond happy.
Biofilters/Biofalls are essentially tanks filled with nooks and crannies – in the form of Bioballs, lava rock or anything else with lots of surface area – where bacteria can reproduce. Having a large-enough biofilter will help those all-important bacteria to thrive.
We also recommend building your pond with gravel on the bottom. Gravel, in addition to looking nice and adding traction on top of slippery liner, gives bacteria even more nooks and crannies where it can grow. More bacteria means happier fish and clear water.
4. Resist the urge to power wash
You can give your pond a head start on algae control by physically removing string algae from your rocks. There’s a big difference, however, between pulling up a few handfuls of gunk and dragging out a pressure washer.
Washing your rocks will remove pieces of the ecosystem that your pond has spent so long building up. This ecosystem is so complicated that we can never replicate it with chemicals, so we never want to scrub or pressure wash rocks or anything else in the pond to the point where we get rid of that ecosystem entirely. It will come right back anyway.
If you must give your rocks a bath, remove debris and gunk as gently as possible and rinse them with water from the pond instead of a hose.
5. Embrace flower power
“Wow!” you might think. “It sounds like this bacteria stuff will solve all my water woes!”
Not quite. Remember, when bacteria eat algae-enabling nitrites, they produce nitrates. These nitrates feed a different kind of algae: that stringy, fuzzy stuff that clings on to your rocks.
While some amount of string algae is normal for a healthy pond, you can keep it controlled by adding a wider variety of plants to your water. Different types of plants will eat different kinds of nitrates. An iris will suck up one kind, and a lily will consume another. A blue flower will chow down on one, and a pink flower yet another. A plant that blooms in May will eat a different kind than one that blooms in September.
These plants will work together to prevent algae from growing in the first place, so you don’t have to worry about killing it later.
6. Cut back on fish food
Your fish won’t get fat if you overfeed them, but excess food will harm your pond.
Aquatic critters like koi and goldfish can largely survive on the mosquitos and other pests that might otherwise take over your water feature. When you supplement that diet with flakes or pellets, only feed as much as your fish will eat within a couple minutes. If excess food is floating toward your skimmer at the end of a feed, you’re overdoing it.
Why does it matter? Extra food will decay, creating a bad environment for your fish and a good one for the kinds of chemicals that will muck up your water and potentially kill your pond life.
7. Don’t add too many fish
Fish are a crucial part of your pond’s ecosystem, but you can have too much of a good thing.
The amount of fish you can keep in your pond is determined by the size and efficiency of your filtration system. When your having difficulty keeping your water crystal clear or getting excessive string algae, that may be an indication that your filtration is inadequate and it’s not able to handle the debris, the fish waste, and may not be providing enough oxygen.
If you find yourself with too many fish, it’s time to improve your filtration system.
Speaking of fish, they need to breathe just like you. Keeping their water properly oxygenated will keep them alive and your pond water clear.
Make sure to clear any leaves and other debris from your water regularly to stop it from decaying and filling your pond with ammonia. This is especially important if your pond does not have a mechanical skimmer that does much of this work for you.
You’ll also need to keep an extra close eye on your fish during the summer, when the warm water has a harder time holding on to oxygen. Consider adding an aerator at any time of the year if your fish appear to be gasping at the water’s surface.
9. Watch your pond’s surroundings
Is your water cloudy or brown? Your problem may have an easy solution. Look for external debris that might be washing into your pond, like fresh mulch, pollen, tree sap or soil.
10. Think carefully before adding algaecides or other products
Algaecides remain one of the most popular options for ridding ponds of green gunk. They provide quick results and seem to treat the problem at its root.
But be careful.
Algaecides do not treat actually treat the main cause of your water problems, just the symptom. They can also kill your fish and plants if you accidentally put too much in.
We believe that almost all water quality issues can be treated using the methods listed above – without using harsh chemicals.
Another product your pond doesn’t need: algae-killing UV lights. While they won’t hurt your pond life, we have never in our 30 years of pond-building experience had a need to install one.