A Case of a Severe Fish Pond Algae Problem

The following story is that of Robin Crofoot's.

Robin lives in Germany and his tale represents a larger version of what many pond keepers experience... dirty murky water that poses no real problem for the fish but is a source of annoyance and frustration for the pond keeper. This frustration is associated with algae formation in the pond.

There is one common denominator when it comes to algae problems in ponds and that is the algae is present because the water contains sufficient nutrient that allows the algae to thrive under warm water and good sunlight conditions. The most important nutrient to sustain a thriving algae community is what is called Nitrate. Nitrate compounds are dissolved in water and are the result of (a) fish metabolic processes and (b) the water used to fill and top up ponds. In some areas Nitrate levels in tap water are very high. Robin uses borehole water sourced from an agricultural region (farmers use nitrate fertilisers and as a result nitrate gets dissolved in run-off water and finds its way into the water table).

Getting Rid of Suspended Algae

Given a suspended algae problem there are 2 approaches to removing the algae that causes murky pond water. These are

1. Install an UV Clarifier of the correct size and this will control the algae by killing it as soon as it is formed which means the water must go clear. This is where the correct sizing is vital because if undersized the UV will not be able to kill the algae quicker than it is formed and the pond will remain murky. Most UV specifications on manufacturers boxes are OVER STATED.

2. Remove the Nitrates dissolved in the water. Unfortunately this is not an easy process. However there are bacterial products available that will do this by working in anaerobic areas that occur to a greater or lesser degree in all ponds.

Here's Robin's story and my responses... to learn all about how algae forms and how to remove it using Viresco then visit the following site and download the PDF ... click here . When you get to the site navigate to the Aquatics Products page and download the catalogue

Robin's Tale

Hello Tony,

Greetings from Germany. It has been 5 years since we corresponded and I am sure you do not remember me, so taking a risk of boring you, I will give you a quick update.

2003 – built my pond out of cement – LATER, found your and bought book (too late). The first year I had problems with dead Algae making weird columns of yuck in the pond. The first winter the cement cracked letting out almost all of the water (-20 Grad) and I put my fish in a barrel on the terrace until spring.

Spring 2004, installed a plastic liner – all problems seemed to go away, and I was satisfied with the outcome, but hated the appearance of the black plastic. All went quite well through the winter of 2004, spring and winter of 2006. Plants growing nicely, water always clear. Spring 2007, a hurricane blew through, ripping the roof off the barn and throwing it (of course) in my pond, ripping the plastic liner to shreads – overnight water “gone”. Removed the plastic (no money to replace it – 4x4x1.5 meters), plants, and all debris and repaired the now highly visible cracks in the original cement (probably due to settling over the years with the liner installed). Winter 2007, pond ok, did not crack in the extreme low temperatures.

Spring 2008, has been anything but “normal”. HOT in May, cold in June, July was a month full of storms, August was HOT and DRY. About 20 meters away from the pond grow 5 Beech Trees that dumped literally tons of their tiny seeds in the pond during the heavy winds. August, my entire system was overloaded. Water went green. I had a new UV light in spring installed, but thought it went bad. Bought another bulb, not any better, so bought a second entire UV unit and installed it in series in my filter system. Water still extremely bad! Drained pond. New water. I can only fill using my well, about 350 liters a day in a 16,000 liter pond. It takes many days before it is full again and by then the water was bad again.

Filter system is 3 part. My main pump goes through the first UV light, through the second UV light, then into a series of valves, that distribute the water in 3 directions. One goes into my stone waterfall, which is divided in half, with the water coming in the back side, (from the bottom), goes through rocks, sand, hair curlers, pipes, and anything else I could find – then goes over the top into the waterfall area and back in the pond. The second valve sends the water through a 1x1 Meter, 5 chamber filter that is filled with various density of foam (should be more than enough for this small pond – all by itself) – then empties into a barrel filled with wool filter material, then back in the pond. The 3rd valve sends the water through a plastic square “bucket” that has heavy wool blankets that the water goes through from the top as the blankets are above the water outlet (suspended, not immersed). This filter is clogged every other day, with green “mud”. I have 20 small fish in the pond.

The water gets worse every day. It is not Algae that is living, but dead Algae that the filters do not catch. The pump is a pump for use with a waterfall and pumps a tremendous amount of water, I think that the 16,000 liters go through the system 2 if not 3 times a day. I can not get a grip on this dirty water.

In the afternoon, the dead Algae (in some places it is about 2-3cm deep) – rises to the surface in “chunks” – or remains suspended. I have a surface skimmer, but when this stuff goes through the net it dissolves again. I have only one very large lilly pad plant in the pond and a few “grass like” plants taken from local rivers. I am afraid that a lot of plants will with their roots crack the concrete. I don’t know if water plants do that or not but when I took the plastic liner out, I had to pull one lilly pad out with the truck as the root system had “taken over” the pond bottom in only 3 years.

I am not one of the “rich and famous” and build most of my stuff myself with materials “on hand”. Up to this summer all has worked very well, but now all is a disaster.

The bio-system seems to work quite well, and the water is clear, but extremely Dirty. Do you have any ideas on filter material that will catch the dead Algae better than the system I have in place?

I am at wits end and have threatened to fill the pond with sand and raise lizards. Ha.

Thanks Tony for any advice. Have a great day and smile.

Sincerely,

Robin Crofoot

Rossow, Germany

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Hi, Robin

I remember you well and sorry to hear your tale.

From what you have described I can think of no other way of filtering out the algae… however it sounds to me that algae is still being formed and that’s why you are not seeing an improvement. As fast as you’re removing it it is being formed again.

Algae thrives on nitrate … if nitrate can be removed then algae cannot be formed.

I suggest you download a pdf document this link. It tells you a lot about nitrates and algae and is written by John McLaughlin (UK) who probably knows more than anybody the problem with algae in ponds.

The pdf download refers to a catalogue link but contains really good pondkeeping wisdom and is far more than a catalogue)

Best of luck and regards

Tony

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Hi Tony,

Thank you for your quick reply. I checked the link you sent, but must wait until Sunday morning to download it due to it’s size. I have a VERY slow old modem and the rates are cheaper for online time on Sunday. 3+Mb will take me the better part of an hour and a half to download. In our part of Germany there is no DSL or even ISDN, just the old monolog system with about 4,6KB per minute. It is the real dark ages.

I am not a chemist, but when you said “Nitrate” I thought “fertilizer”. Hmmm, what could have suddenly changed to create this problem almost overnight. I have thought of two possibilities and am sure that both have contributed to the problem. Our old barn is a yearly nesting place for Swallows, and since we have been here they have multiplied to about 50 birds. There were only about 4 birds at the start. The in and out point to the nesting area is through a broken window in the barn that I have not repaired so the birds can have access. However their “flight path” is directly over my pond. Almost all day long they buzz over the pond, and we have never had a mosquito problem – but I noticed that they also take “bombing practice” trying to “hit the Goldfish” with their “poop”. It of course dissolves in the water. With the extreme dry summer hundreds of wild birds stop daily at the pond for a drink. They leave their mark too. Many of the small wild ponds in the area have dried up due to the lack of rain. We even had a deer come for a drink (that is really unusual). Ok, I don’t mind helping out nature even when they visit our back yard.

The second possible cause is the water I use for the pond. City Water here costs 9 Euro per cubic meter, so I use water from our shallow well for everything that we do not “drink”. With the dry weather it is pumping about 350 liters a day. In normal conditions it has done about 1,000 liters a day. This is a ground water well, and we live in “farming country” – meaning fertilizer is sprayed on the fields – meaning that it has surely made it to the water supply. So, when I drained the pond, I refilled it (not knowing) with highly concentrated fertilized water. Of this I am about certain, as we bought a 4,000 liter “swimming pool” (blow up type) and before it was filled, it had turned green with “sick looking” bubbles and Chlorine did not do much except to make it worse. We drained it and did not use the pool – but it was filled from the same water source as the pond. Then – probably compounding the problem, I have been running water a half an hour each day (for a couple of weeks) into the pond making it overflow – thinking that it would help dilute or push out the bad water, but in reality just adding more nitrates each day.

Cooler weather has arrived and the Swallows have gone south, so that problem is eliminated until next year. So, that leaves two factors – the water source and the lack of plants as compared to earlier years. I can’t do must about the water source, but I can add a lot of plants from our local lakes and rivers. The question is this – will water plant roots destroy the cement pond. I know how quickly above ground (or in ground) / normal grass and weeds, along with trees will go through cement, crack it, and in extreme cases even buckle it. Are water plants as aggressive? I guess I could plant then in buckets or trays (ugly).

I noticed the “NitroGone” tablets that are available, but hate to start using chemicals as they never seem to have an “end” and ordering them from England would get expensive over time.

I have also noticed that when the pond is only about ¾ full that the filter system does a much better job than when it is completely full – of course due to less water to keep clean. What do you think about me removing about half the water, then let it get back to really clean (it is “clear” just extremely filled up with the dead Algae), then adding a little water, letting it clean up, then a little more, etc. until things are back to normal. I am also looking for a used “shallow well pump” to use as a “vacuum cleaner”, just sucking out the green garbage but as of yet I have not located one and new ones are expensive.

I forgot to mention it earlier, but the combination of using 2 UV lights give me 22 Watts for the 16,000 liters. That should be more than enough for “killing” purposes – no?

Thanks for your time and replies. Have a great day.

Robin

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Hi, Robin

You may well be right about the swallows and field fertiliser run off.

The best product I'm aware of that is proven to remove Nitrates is the Viresco product I mentioned yesterday. When you download the info you will understand the importance of nitrates and you will also understand how Viresco works since nitrate removal from water is not easy. Plants alone don't do a good enough job of removing nitrates.

By the way I have extracted the important pages from John's catalogue to bring file size down to 2.1 MB

I have also sent you an invite to a Google email address. I think you will find this email a help in downloading large file sizes.

If you let me know later I can send you the abbreviated download by email

Your UV capacity in my opinion is too low (at best 22 watts is borderline for your system especially if you have high nitrates.)

As far as aquatic plants damaging concrete I have never heard of this but have no practical experience.

An expert on aquatic plants and pond landscaping who will know for sure is Peter May ...  He lives in UK