Algae spores are ubiquitous and unavoidable in a fish pond. Algae blooms are a natural occurrence and the sight of a healthy mat of filamentous algae on your pond liner means your pond is mature
Green water is of no immediate threat to fish. There are some potentially negative aspects however, and both those and algae control are discussed here
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Algae, of which there are many species, are plants [the exception being blue green algae which is actually cyno bacteria]. Of main concern to pond keepers are both planktonic [free floating] and string algae, both from the phylum Chlorophyta
Single celled planktonic algae is suspended in the water and in large enough numbers, cause the "green water" appearance pictured right
String algae affixes itself to any wet surface surface and as the name implies, is a long stringy plant. Variants can also be seen floating in clumps on the surface of the water and is also known as blanket weed
The reality is you can't stop the growth of all algae and have fish at the same time |
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Positive
The impact of algae is not completely negative. For example, string algae can be beneficial as it provides some food for the fish. It also competes for the same nutrients as planktonic algae thereby reducing/controlling green water algae blooms. String algae also hides the liner and producing a more natural look. Algae will also add oxygen to the pond during the daylight photosynthesis
Green water will protect fish from the effects of the Sun and help hide them from potential predators. Additionally, Fish will feel safer in turbid water that resembles their natural habitat. Green water is also key for rearing baby koi as it supports a microscopic food web [zooplankton feed on algae] which fry need to feed on to develop to their potential
Negative
On the downside, it is not aesthetically appealing viewing green water as opposed to beautifully coloured koi. Long string algae growing from the sides of the pond is also unsightly. An algae bloom can also cause water quality concerns. Namely, fluctuations in pH as algae utilizes CO2 during photosynthesis thus elevating the pH [preventing carbonic acid from forming] and DO [dissolved oxygen] concerns
Potential oxygen depletion at night is a real concern when O2 is being consumed by algae and other plants.
Even emergent plant root systems will consume oxygen during nightfall.
This can cause fish in heavily stocked ponds to gasp at the surface and it is best to check for this just before sunrise. Additionally, viewing koi for potential health issues is obviously hampered due to reduced visibility when the water is green. These problems aside, there is usually no need to immediately panic if your pond water turns green. Without a UV this is likely to happen, and it's just as likely to clear up in a few weeks as your filter matures, phosphorus is exhausted and plants sprout new growth
As far as pond plumbing goes, string algae is one of the only things I have seen that can clog a 4 inch bottom drain [ the other being those who fill their planting baskets with small pea gravel]. This can be a big negative requiring a pond dive to clear - a rubber pipe flusher will not rectify the situation
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Coverage like this will control algae blooms at the expense of viewing your fish |
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Planktonic
An algae bloom will not directly harm the fish however it will impede your vision of them. Therefore if an ulcer is developing, you will likely not notice it
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String Algae
String algae has the capability to clog a 4 inch bottom drain as well as being unsightly. A small carpet of string algae is unavoidable and desirable however
Macrophytic Algae
Actually takes the form of a plant [Macrophyte] |
Doing a massive water change is not the solution to rectifying a green water problem. All it does is reset the cycle and kill beneficial bacteria that are trying to get established. The water will turn green again, likely within a week or two
The other mistake people make is scrubbing all the string algae off of the liner. Again, string algae is a competitor to the planktonic algae so removing it will leave more nutrients to create green water algae blooms. It is impossible to stop a nice carpet of string algae from growing on a liner in fish pond so leave it alone, it is beneficial
Algaecides, in particular those based on copper sulfate, are toxic to fish and you dose enough to kill the algae but not the fish - or at least that is your hope. As a general comment, bottled remedies are a band-aid approach at best and can often be detrimental. Certainly some are much safer then others but the bottom line is these solutions should not be your frontline defense against algae
Many tout the "natural eco system" will do it all as plants and fish balance to create clear water. Of course this is possible, however, most hobbyists have ponds that contain a tremendous bio load packaged in a small closed system. Sure 70% coverage with plants will provide clear water. Plants both rob the algae of sunlight while competing for nitrate and ammonium. However, plants in our climate are doing little in April and barely starting established in late May. Meanwhile, opportunistic algae spores blowing in greening up your pond in April. This poor timing occurs when fish observation is critical, koi are coming out of their Winter weakened state and need to be closely watched
In Summary
Leave the pond alone ! Cleaning and scrubbing the liner and doing massive water changes will just reset the cycle and never allow the pond to get established. You will kill zooplankton, many of which are filter feeders like rotifers. They actually eat algae and can filter up to 1000 times their own volume in 1 hour. In the final analysis, plants are not a realistic full season approach to controlling algae - what you need is patience |
There are many ways to limit algae growth but they essentially break down into 2 groups:
The expensive but most effective approach or the less expensive band-aid approaches. That being said, a multi-tiered approach is more effective than relying on just one method Plants, established bio filters, reticulated foam, barley straw, blanket weed controllers & powders, shade clothes, dyes, flocculants, phosphorus removers, aeration and water movement etc, all work in concert to help keep algae in check. But these should be considered ancillary approaches to the foundation of your planktonic algae control, the Ultraviolet Sterilizer
UV's are expensive but investing in one is really the only way to proceed if you are serious and do not want green water at any time. Not only will a UV kill and cause clumping of planktonic algae, it will also sterilize the water by killing bacteria and viruses. Obviously very beneficial [see the chart below]
As for string algae, it normally will stay in check on its own [with the help of the fish consuming it], remaining 1-2 inches in length. If not, manual removal and then treating with a product like "Pond Balance" is my recommendation
Water falls are particularly prone to string algae due to the water flow and nutrient load coming out of the filter. These can be covered [black tarp] and salted for a couple of days to kill the algae and provide some residual control |
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Clarke Koi Ponds are distributors of Delta UV's EP line of pond Ultraviolet Sterilizers. We prefer these units because they operate very efficiently utilizing just 1 bulb - therefore bulb replacement costs are lower compared to other manufacturers.
They achieve this with a 6 inch diametre stainless steel body that allows for a longer dwell time [exposure to the UV light]
Another key feature of the EP Series of UV's is the pressure switch which automatically shuts off the UV bulb if the pumps stops functioning. This prevents heat buildup [and potential damage] from a bulb that is not being cooled properly with the water flow |
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| Bacteria |
µW/sec/cm2 Required to Kill |
| Aeromonas |
3,620 |
| Clostridium tetani |
20,000 |
| Pseudomonas aerginosa (environmental strain) |
10,500 |
| Salmonella enteritidis |
7,600 |
| Streptococcus hemolticus |
10,000 |
| Algae |
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| Chlorella vulgaris (algae) |
22,000 |
| Virus |
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| Hepatitis Virus |
26,100 |
| Influenza Virus |
26,100 |
| Rotavirus |
24,000 |
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