A Pond In The Sun

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In the midst of summer, it’s a common question. How much does sun exposure affect algae growth?

And like most answers, the correct one might range from a little to a lot. Isn’t that always how it is? Every pond is different in how it responds to sun light and for some ponds sun light exposure is one of the primary issues.

More accurately, large and deep ponds tend to have less of a problem with sun exposure. Small backyard ponds and even large, shallow ponds can be problematic regardless of what other treatments might be used to control algae growth.

Like all plants, algae (in all it’s forms) can thrive with adequate exposure to sunlight. But light isn’t the only thing it needs to grow. Algae must have adequate nutrients in the water to support it, and when this is coupled with sunlight, most algae types can grow very well.

Now before we go bashing sun light as a bad thing, keep in mind that most fish do best with some sun exposure. Also if you have a water garden with desired plants, these need a fair amount of sunlight each day.

What’s right for your pond? Well for koi and fish ponds, usually a few hours a day is fine. All day sun exposure is not. For water gardens, you can expect to up the amount of light to about 4 to 6 hours a day.

For small ponds the most logical and natural way to control sun exposure is to use desirable plants such as lotus or water lilies. These provide a form of shading to the pond and for fish if you have them. These plants also serve double-duty by absorbing the same nutrients that algae would normally feed on. This is why plants would be a preferred method of “shading”.

Keep in mind as well that a few plants here or there, may not be enough. Some pond experts suggest covering up to two-thirds of a pond’s surface area with plants. This may be more than some owners would like to see in a pond, but the choice is yours. If you don’t want to use that many plants, other options include using aquatic pond dyes, or even structural shading.

I’ve recommended in the past that folks with very small ponds actually use a good sized garden or patio umbrella for light control. Other pond owners have planted trees around their pond to block the sun, but remember that it will be important to keep falling leaves and other debris out of the pond on a regular basis.

Large ponds are obviously harder to cover but normally when algae is present in a larger pond, the main culprit is high nutrient loads due to run-off or organic debris build up at the bottom of the pond. The exception to this is very shallow bodies of water that tend to be very problematic with algae issues.

In large ponds that are six feet or less in depth, the best option to control algae growth is a combination of aquatic pond dyes and beneficial bacteria. The dye restricts light penetration in to the pond and limits it’s stimulating effects on the pond bottom. The added shading also helps protect the natural bacterial activity in the pond as well, as some bacteria can be stressed and negatively affected by high temperatures and long running sun exposure.

One final tip for large ponds involves the dosage of pond dye products. While you can follow the suggested dose instructions on the bottle or package, you may want to experiment with the amount of dye you use at one time. Sometimes simply lightly tinting the water is enough to have a positive effect and most folks don’t find a blue looking soup to be very attractive. So one suggestion is to go with the idea that maybe a little bit of dye will go a long way and feel free to experiment a bit on dosage to see what provides a nice balance of appearance and effective algae control.

No matter what size of pond you may have, sun light can be a great blessing to the overall health of the pond. It can also be a strong stimulant to unwanted algae growth if certain conditions exist. Fortunately for you, now you have several options to aid in the cause of sun exposure and algae control, and all of them are relatively inexpensive and safe options to investigate.

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15 thoughts on “A Pond In The Sun”

  1. Hi Michael,

    Mainly the other issue is high nutrient loads. In small ponds this might be from high levels of fish waste or too many fish in a pond for it’s size.

    In larger ponds most often this would be an accumulation of organic debris in the pond such as decaying leaves, dead algae, or perhaps fertilized runoff.

    Any thing that creates or raises nutrient loads in the pond along with the stimulation from excessive exposure to sun light can make algae much harder to control.

    By working on these two factors though most pond owners can make progress in the battle.

    All the best,

  2. i have a small, six foot round, 18 inch deep cement koi pond in my yard–i am very proud of the water quality that i have been able to maintain

    i prefer natural methods to keep it clear but i have a big problem with an ever richer green colored water

    what method do you recommend to keep the bottom of the pond clear of debris?

    in addition to water lilies, water lettuce and a recent addition of underwater plants such as hornwart (?) and some kind of grasses and leafy things,i have two large, flat filters hooked together to my intake valve at the bottom–i use them with a combination of charcoal and filter sponges, plus the external biological filter (no uv lite) and your enzyme packets in the pond—chemicals do work, but if I don’t keep the pond loaded with them, the water seems to turn a darker green faster and faster–i really don’t like to use them

    please help

  3. Hi guys, I have found one product that cleared
    my pond up from the algee.. ” No Bugs”
    three days after I used this product MY POND was clearing up I could actually see the Koi!!
    Hell, it had been four months since I saw them.
    I wasn’t even sure if they were still there.
    I had just about given up hope till I found this product. It killed the algee problem
    The mint plant that is gowing in the pond keeps the little critters happy from the root system == food. Enjoy your critters!!!
    John Eversoll

  4. Hi,
    I have a large (not huge) pond about 1/4 acre. What is the “No Bugs” product? Would it work on a pnd the size of mine? Thanks for the info.

  5. As I write this, my husband just removed the fish from our pond and is powerwashing the algae from the rubber liner in our small pond (about 350-400 gal.). Algae has become a thorn in our sides every summer (we drain in the winter). We’ve even thought about filling the pond in with dirt and planting grass. Instead of enjoying the sights and sounds of the pond, we have become slaves to it.

    Can anyone help?


  6. How does the water quality like the PH factor affect the effectiveness of beneficial bacteria? Are there other factors that affect the ability of beneficial bacteria?

  7. Hi Larry,
    Well pH can have an effect on the bacteria to some extent. Most bacteria do better the closer you get to say 7.5 or so. Also oxygen levels in the water make a difference too.

    Since bacteria are living things it make sense that the same things that offer good support for other aquatic life would also provide benefit to the bacteria.

    E. I guess my first question is…what have you tried so far?

  8. I have a 3,000 gal pond and have an ultraviolet light but with the high temps, it seems like the pond is always green in the summer. I have large koi and they don’t seem to mind it, in fact they are thriving and have spawned the last 3 years. I have some baby koi this year and hope to sell them and maybe get some money for the koi food. I would also like to know where to get the “no bugs” and find out how it works.


  9. Hello,
    Wow great post. I too have had string algae problems, and the rake method does get the bulk of it out, but be carfeul of the little creatures living with in the algae. I am leaning towards the not adding chemicals of any kind. But introducing more pond plants to use up the nutrients, and limit surface water from entering more nutients.
    Thank You
    Darrell D


  11. I “inherited” my pond when the one who set it all up moved away! I knew nothing about maintaining it, cleaning filters, keeping the water quality good, getting rid of algae…

    I clean the filters when the water coming down the waterfall seems to be getting less forceful and periodically clean the debris out of the water bell pipes to keep it flowing evenly.

    As far as algae is concerned, adding more plants and some large snails has taken care of the problem completely. I have a little bit of string algae I clear out with my net every now and then, but the water is crystal clear, the koi are thriving, and I haven’t had to use any chemicals whatsoever. This spring, the algae was so thick I had to empty the pond and scrape the sides with a credit card to get it all off. Adding the plants and snails took care of the residual over a period of a couple of months and now it’s gone.

    I was like the person who considered filling it in with dirt and planting flowers! But I’m glad I stuck with it and I enjoy it every day. It’s a lot of work, but worth the effort.

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