Cilindrical pond oddity

[Woland]

I have in my garden a pond, which is in fact a reinforced concrete cilinder which once (30-odd years ago) contained an outdoor tank for heating oil. The tank having been removed, the cilinder was probably deemed to difficult to lift out of the ground, and turned into an ad-hoc pond. With dimensions of 1.8 m in diameter by 1 m deep, it has a volume of approximately 2,500 liters. It is home to a few potted plants attached to the sides, some free-floating water soldiers (Stratiotes aloides), an acceptable number of salamanders, frogs, insects or their larvae, and enough algae to drown a mule in. Maintenance is limited to me scooping out the algae and floating gunk once a week, and any sunken stuff once or twice a year.

So, here's the thing: what can I do to get rid of the algae, and create a pond that looks as hospitable to water fauna as it actually is? Do I need a pump and filter, or can I get by with simpler means? Do I need to partially fill the pond with rocks to improve its surface-to-volume ratio? More plants? The pond's location is mostly sunny, with the shadow of a large beech moving over it in the afternoon, but direct sunlight barely reaches the bottom even this time of year.

 

[Woland]

Here's a couple of pics to give you an idea. Water level is at the brim right now, but can easily drop 20 cm during a hot, dry summer.

 

[Stephen Noble]

Welcome @Woland! You have an interesting pond. If I understand, it is about 3-feet deep and roughly 6-feet in diameter and is completely constructed from concrete. Has the concrete been painted or coated with anything such as an epoxy coating? I ask this because fish can sometimes be difficult to keep in untreated concrete. However, if the concrete has been soaking for many years it might not be an issue.
To answer your questions:
Yes, it can be a nice home to native species especially frogs and turtles. A floating island in the middle will attract both.
No, don't make the pond any shallower. You need the depth for a winter hard freeze. Any overwintering animals will need the depth and also some way to keep a hole in the ice for gas exchange.
Aeration will help reduce algae.
Personally, if it were my situation, I would build a decorative bog filter next to the pond and create a waterfall with the returning water. The bog will greatly help with algae and remove excess nutrients.
Looking at your images, it appears the pond is at ground level with your yard. Possibly, runoff water is making its way into your pond and if so, that most likely could be contributing to your algae situation.
A pond needs more than a couple times per year of TLC.
Please let us posted with your plans. We are happy to help.

 

[JRS]

Seems like you have a successful classic wildlife pond...which is not always the prettiest from a water clarity standpoint. To help clear algae and murkiness from a pond, I 'd second Stephen's suggestion of a bog filter, worked wonders for my green water algae.

 

[Mmathis]

Bog filter and aeration, as stated above.

 

[GBBUDD]

Welcome,
I would agree with the bog, A bog is nothing more than pumping water from the pond to the bottom of the bog. if the bog is long youll need a way to get the water to evenly folow accross the bottom so as it rises it does so evenly through layers of rounded stone/ river rock

 

[Woland]

Thanks for the replies. You've given me some things to consider, and some things I need clarification on.

As far as I know, the concrete is untreated, though 35 years after the conversion to pond, I don't think it matters anymore. Also, I have no intention of putting in fish or turtles - this is a pond for amphibians and nothing else. In that same vein, no solution to increase the quality of the water should create too much water flow.

Winter temperatures don't really drop that low here - past winter we had less than a week of daytime freezing, and the last really cold winters were those of 2010 to 2012, thanks to a certain Icelandic volcano erupting.

I had considered garden runoff being a problem, so a few years ago I lowered the ground level around the pond where possible, and partially replaced the soil by the rocks you can see at the bottom of the pictures. This made the pond more accessible, but didn't have much influence on algae growth. It remains the local low spot, however, and excessive rainfall probably remains a problem. As for TLC - had to google that - I've never added anything to the water.

And you can't tell from the pictures, but the pond is actually at the higher part of the garden - the house is built on/into an incline. The driveway you can see at the very top of the pictures is about 2.5 m lower than where I'm standing.

This leaves me in a bit of a conundrum regarding a bog filter. One on the left side of the pond would be most aesthetically pleasing, and would catch the most sunlight, but that location is home to the root system of a cotoneaster covering that part of the incline. I'm not willing to get rid of those plants, and the whole amount of space available is only about 1.5 square metres. There's more room on the right side, but that lies more in the shadow of the beech. So much shadow, in fact, that the roses currently located there have started dying off and will need to be replaced with something more fitting. Sunlight reaching the pond is from about 9 am to 3 pm, and then again after 7 pm. A bog filter on the right hand side would be shadowed from 2 to 6 pm. I'm not quite sure what the effect of this would be.

 

[JRS]

For a shaded bog, hostas come to mind, some here have used them.

As for TLC, I believe he may have meant Tender Loving Care, as in regular attention and maintenance to keep it clear, not the pond products company.