Water Garden & Features Q & A
Q: How do I control algae in my decorative pond, both long term and short term?
– Stefanie in Michigan
A: Algae blooms are the bane of most pond owners. All summer, they rear their green heads and turn a beautiful pond or water feature into a soupy or stringy mess. But with some planning, both the floating (pea-soup algae) and filamentous (string algae) species can be controlled in the short term and prevented in the long term. Here’s how:
To get your decorative pond looking clean and clear right away, you’ll need to knock down the algae population by using a chemical herbicide, like AlgaeFix® or TetraPond’s® Algae Control. These algae-busters are safe for use in ponds with fish, but because they destroy algae so quickly, they can cause a drop in oxygen levels in your pond, especially during the warm summer months. Be sure that your pond is adequately aerated with a fountain, waterfall or underwater air diffuser.
To prevent that green goo from surfacing again, you need to limit its food source: Nutrients. Algae thrive on nutrients, which are the end product of the nitrogen cycle. The nitrogen cycle begins with ammonia released from fish waste and detritus. Nitrifying bacteria turn the ammonia into nitrites and then into nitrates (nutrients). The algae grow, the fish eat it and excrete it, and the cycle begins again.
So, how do you control the algae’s food source?
Try these approaches:
- Keep your fish load to a minimum. Most pond owners love their fish, but if they plan to have 60 12-inch koi in a 1,000-gallon pond, they’re going to have an algae problem – which can be expensive to manage. So, when calculating your fish load, think of it in pounds of fish or total inches per gallon. Remember that your fish are growing and possibly multiplying, so plan for the future and remember: Less is best. Be careful not to overstock your decorative pond.
- Increase the number of aquatic plants. Whether they’re submerged plants like hornwort, marginals like dwarf bamboo, or floating plants like water lilies and water hyacinth, aquatic plants consume the same food that algae does – nutrients. The more plants, the more the algae have to compete for those nutrients. Floating plants also shade the pond, which filters the sunlight and can slow the growth of sun-loving algae. You should try to cover 40 to 60 percent of your pond’s surface with floaters.
- Check the filtration. The size and type of filtration system on a pond will depend on the fish load. If the filter is not properly sized for maximum potential, the fish will outgrow the filter and produce unhealthy amounts of ammonia, which could prove lethal to the fish. An inappropriately sized filter can also cause an algae bloom from the copious amounts of nutrients in the water. In most cases, filters on the market are rated for ponds containing no fish or a minimal fish load, so you should consider a filter that is rated for at least two times the water volume of your pond.
- Toss in some beneficial bacteria. In addition to ensuring the proper mechanical filtration, you may also consider adding some additional biological filtration – beneficial bacteria – to your pond. These hungry creatures gobble through nutrients, breaking down fish waste, leaves and other organics that accumulate in the pond. One product to try is called DefensePAC® by Pond Logic®. It’s a combination of five products that provide beneficial bacteria, trace minerals, and a fish and plant-safe pond cleaner.
No pond will ever be completely algae-free, but the key to keeping the green stuff under control is to limit its food supply. Like any other living thing, if it can’t eat, it can’t survive!
POND TALK: When was your worst algae bloom, and how did you correct it?