Summertime & Green Pond Algae. How To Have A Crystal Clear Pond This Year

When shallow pond water warms up then beware of algae blooms. Before I comment read this letter received from Sharon this week. Sharon lives in USA. .Koi and goldfish dying in green algae pond ... need an UV and pond filter

Hello,

My dad has a very large goldfish pond that is about 20+ years old. Late last summer he started losing his biggest koi one by one. This year now that the weather is getting warmer again he is started to lose his biggest gold fish (maybe 4 per day). His pond is

5 1/2 feet deep, 6 feet wide and 6 feet across. He has a lot of plants, but it appears to me he also has a lot of algae buildup. His water has a dark green tint to it. He leaves his water falls running 24/7, but the goldfish are still hanging around the top of the water. Some are even raising their heads an inch above the water for oxygen. There is obviously an oxygen problem in the water. My question is....do you think it is the algae? Or...could it be the waste and debris at the bottom of the pond? He tried cleaning the "gunk" out a few years ago by hand....but it was a major - stinky task. He doesn't have much money to spend on an expensive remedy, so I was hoping there may be something else we can do.

Should we buy the algae killer stuff that turns your pond blue? Would that help? He had the water tested and there is a slight raise in ammonia (which I know can kill the fish too).....any advice you can give would be greatly appreciated.

I think he needs to clean the stuff out of the bottom, but what's the easiest way? and killing the algae? What's recommended?

Thanks, Shannon

My Reply

Yes you have a major algae problem by sounds of it ... the algae compete with fish for oxygen especially overnight. Read this article here

http://www.practical-water-gardens.com/pyjamas/article010co2.htm

Summary of article ...

Think of your pond as breathing in oxygen during the day and breathing out carbon dioxide at night

Carbon dioxide pond problems can be controlled by waterfalls, aeration and uv lights. Carbon dioxide in pond water results from a number of sources including:

1. waste products decaying at the bottom of the pond

2. respiration by pond inhabitants .... fish, insects, plants, algae

Of course all of us think first and foremost of oxygen in pond water as being essential and of course this is very true. Carbon dioxide is also of critical importance. Oxygen and carbon dioxide also work in concert with each other.

In simple terms as carbon dioxide levels increase in a pond then oxygen levels tend to decrease. This follows a natural pattern as can be seen in the sketch. Here you can see that from dawn to dusk (daytime) oxygen levels in pond increase and decrease again from dusk to dawn (night). Carbon dioxide concentrations in water act in reverse - falling during daylight hours and rising during the night. Oxygen levels are at their highest at dusk and carbon dioxide levels are highest at dawn.

Beware algae blooms in ponds ... this is what is happening in Sharron's dad's pond

Let's equate this to what living organisms do in the pond. Think of the flora and fauna as exhaling carbon dioxide while inhaling oxygen during the night.

From this you will agree that dawn is the critical time in a pond. Often people wake up to find dead fish and wondered what happened. Such deaths could be associated with very low oxygen levels coinciding with high carbon dioxide levels. When ponds are full of suspended algae such problems can arise.

If there is a very small amount of algae bloom in the pond then you will find oxygen and carbon dioxide levels will not change significantly between early morning and late afternoon. On the other hand dense pea soup type water will show very significant variations.

Seasonal Impacts upon carbon dioxide problems

The first thing to realise is that oxygen concentrations are highest in winter because water is cooler. This means the concentration of oxygen can be higher. Because oxygen concentrations are high the oxygen reserve is not depleted so quickly during the night. Plant and animal life has also slowed down significantly.

On occasions fish in ponds with no fountains or waterfalls may look listless in winter due to carbon dioxide levels being excessive but this is normally associated with a long run of calm dull days - in these circumstances there is no natural wave action to allow oxygen to be transferred to the water. The problem quickly sorts itself out when windy and bright weather returns.

In summer water can hold much less oxygen and the animal and plant life (algae) is also thriving due to higher temperatures along with more nutrients in the water associated with feeding fish. The living organisms are therefore emitting more carbon dioxide in a situation of potentially disastrously low oxygen levels . Fish then die from suffocation.

Sharon, You need a biofilter and UV urgently I suggest you take look here

http://www.practical-water-gardens.com/sitedirectory4.htm  or use links on this page

UV kills algae 100% effectively and results in clear water when sized properly

No fish pond should be without  pond bio filter and you MUST clean out the gunk on the bottom of the pond ... if it stinks to you imagine how the fish feel living in and around the mess 24 hours per day

By the way goldfish are far more tolerant of poor water conditions than koi and this is reason probably for koi dying last year and goldfish this year. Of course fish have also put weight on so they are also producing more nutrients making need for bio filter even more important