Summer & Blanket weed (string algae) Floating To Water Surface

Robin in Germany wrote to me with his pond problem which is an extreme one in my opinion and well worthy of sharing with all other readers worldwide, owing to the apparent severity and rate of growth of what I believe to be a blanket weed problem . Please also see see Robin's previous letter.

Robin sent me a photo and I can only compare what I saw to "Triffids" ... all those people less than about 55 probably won't understand this term which refers to an out of control plant species in a book called "The Day Of The Triffids" by John Wyndham

Since I first wrote this article I have discovered a British product that is a saviour for people with string algae problems in their pond and I would highly recommend such sufferers take a good look at this pond algae website

Here's Robin's letter and my reply which is based upon the assumption the problem is blanket weed (in the first letter Robin provided detailed observational details) ...

Dear Tony,

Greetings from Germany.

It has been almost 3 weeks since my last letter, and I wanted to update you on what I have done. Directly after my last letter we had another cold front move in, and the temperatures at night dipped under freezing and with cloudy days, the high temp was 10 or below. The water temp in the pond cooled to 8 grad c. The junk floating in the water all settled to the bottom, and the water remained clear and not dirty (suspended objects) for several days. I would run to the pond when the sun shined even for just a few minutes, and observe what was happening.

When the sun shined it would warm the PLASTIC areas that were not covered with sand or rocks, and the tiny hair like whatever (a word fails me) would start growing immediately (you can see that in the picture). Actually it is dead Algae that is just sticking together. When the water warms (late afternoon) these hair collections will shoot to the surface like being shot out of a gun and continue to collect together. (That is the stuff floating in the picture). The picture is HIGHLY magnified (zoomed with a polarized filter so you could see exactly what I am talking about in reality the stuff is very small and hair like).

The nights are still cool (5-7 degrees) and by morning the water would be settled and clear. Then as the sun comes out and the plastic warms, the entire process starts over, and by late afternoon the surface looks like a stopped up toilet, and the hairs that have not reached the surface are suspended giving the water a very green color (NOT like green pea soup). The water is clear, but dirty!

It is necessary to clean the filters 2 times each day, or they clog up like a green mud, and I have had to take the pump apart twice to clean it out (since writing last).

I am trying my best not to change the water, as I would like to find a solution to this problem.

Observation These hairs form only on the plastic area, not on the sandy areas. However, during the evening settling process, this debris covers everything!! My lily pads (are still trying to grow out of the winter dormant stage and are still totally under the surface) leaves are so covered with this debris that 3 plants have died, even after I have tried to gently brush this stuff off the once large leaves. This debris of dead Algae has killed the water grass, and only a few plants are doing well. My bigger fish swim (chase each other) during the day, and come close to the bare plastic areas and stir the debris, which goes suspended through out the entire pond. Even if I drained the water and replaced it, I dont know how I would get the remaining debris out without making a bigger mess than I now have. For several days in a row I have run fresh water in the pond, forcing it to overflow, and it takes the floating debris out, but does very little for the suspended stuff.

The picture was taken today, and you can see that very little forward progress has been made. The UV light is new and has been working for about 8 days. My pump, as I remember from the box, pumps around 7,000 liters and the pond is only 14,000 liters. It should have easily removed the suspended debris, but it has not. A LOT gets caught in the hard particle portion of my filters, but if I do not wash them at least 2 times each day, then the filters go to the overflow and the water just runs unfiltered back into the pond. I did not have this problem last year when the pond was cement only. Could something be wrong with the plastic liner?

Idea (for your approval). When I bought the liner, I also bought a liter of glue in anticipation of future repairs. What if I let the water level down below the bare plastic area paint this glue on the bare plastic, and immediately throw sand on it. Then (I think) the sand would stick, and the problem of too slippery would be solved. I also think that the debris forms and shoots up from the bare plastic areas, because the black plastic warms up much quicker than the protected plastic (covered with sand or rocks).

Other than that, I am about at wits end, and have no other ideas except to slow the water flow into the filter and waterfall, giving the light a little more time to work (although I think it is doing the job ok). As always, thank you for your time and advice.

Your friend,

Robin

Dear Robin

I cannot find the reference I had to University guy ... so here are a few more comments from me

I do really think your problem is blanket weed. Consider the following aspects of blanket weed, also called filamentous algae or string algae (under microscope you see long chains of single cells all joined together....

Grows rapidly and outcompetes other algae and hence water is clear ... because the string algae does not have roots it can only source its food from dissolved nutrients and it needs a lot to grow in abundance

During daytime blanket weed grows by virtue of photosynthesis and attaches itself to any substrate (eg your liner) in long strands ... ie liner is acting as anchoring point for string algae and the anchor is by its nature very weak because blanket weed does not have roots

During daylight hours and especially as temp warms up and sun comes out oxygen is produced ... sun + warm water = more oxygen + faster growth of blanket weed. The blanket weed "string" is thus floated up to the surface where it dies and forms clumps of green yellow algae. The clumps float because of trapped oxygen. Once oxygen has been lost then some algae may sink

Your smooth liner may be bad at providing a more sustainable anchor ... unlike plants which also get invaded by the algae (plants are a much better anchor point) and from which the stings do not easily break away. The result of this is that in time the string algae causes the death "by strangualtion" as it were of the plant

Fundamental cause of big blanket weed problem is nutrient excess as mentioned previously. Can you collect rainwater from roof and gradually use this to replenish pond water?

Shallow water favours blanket weed formation because of tendency to warm up and high sunlight penetration. Do you see formation at bottom of pond or is there more on sides ... ie closer to surface where more light enters

Putting lot more plants into pond will help by converting nutrients and also forming a barrier to sunlight in parts of pond

You will know from fly-fishing that alkaline waters (chalk streams) favour algae growth ... is your pond alkaline? Under these conditions blanket weed growth can really accelerate.

Whatever you can do to reduce sunlight penetration (hence more plants) will help ... days in Europe also getting much longer

If you continually add high nutrient water from your borehole this will worsen your problem Bear this in mind ... stop continuous flow into pond and rely upon biofilter

Let me know what happens with time. Any feedback I might get from UK I will forward to you .... no simple or permanent cure for blanket weed and if barley straw works it is not an instant short term cure. If you read report I sent you will see they are approaching problem as a 3 year experiment