Algea in water supply

I have been looking through the threads here and have not seen anyone discuss this subject so I thought I’d ask.

Since last year I’ve collected rainwater for watering my trees and during the season I noticed a build up of algea in the containers (2x210 L). It is not a whole lot, but the pump is covered in a thin layer and it is visible in the bottom of the containers. By autumn I also stated to see algea like growth on the soil of some of my trees in soil with poor drainage - it stays wet longer at it seems like the algea can grow in this.

I’m wondering if this is something I should try and do something about, and if so what I could do. The water will never be super clean as dirt is washed off form the roof and into the drainpipes, but I’m wondering if there is something that could be added to the tanks to clean the water IF the algea is an issue for the trees that is.

Any thoughts on that? Your input is much appreciated!

1 Like

Make sure the container you collect your water into is covered and light cannot penetrate. Algae will only grow if there is light hitting the water. Hope this helps.


Thank you for your reply!
The are made of a dark green plastic and both has covers.

Do you know if the algea could pose a problem?

In wouldn’t like to say. My knowledge of algae is super limited. What I do know is that it needs lots of moisture to survive

I would not so much worry about the algae. Anything you use to kill/ slow it down would also affect your moss, and maybe trees. A little pump and a filter (?) is overkill. Algae is everywhere…water and sun is all it needs. Anything “fertilizer” just encourages it. Probably growing on any bench that stays wet.
What kind of roofing material do you have? Asphault would be kinda bad for the trees…

Thank you for your replies!
Kurt - it makes sense about using something in the water to get rid of it. I’m not thinking about that as an option.

What do you mean is overkill? I’m not sure I understand.

The roof is black tile, made from concrete of a sort I think. I doubt it is actually asphalt though. Why would that be bad? Is it something I can test for in the water?

Concrete, ceramic, slate, great for what you are doing, collecting rainwater.
Dont worry about the algae. If you are, a small impeller pump with a large 20 micron cartridge filter should remove it for a summer. (It will eventually plug.)] Pump should be high enough flow to use a small tubing hose to water with.
I was thinking about setting up a flowthrough reverse osmosis for my trees. It creates other problems, though. We DID have the best tap water. Then developers moved in. Chloriation is nasty on potted plants… I have 140+ trees.

Great input Kurt. Thanks.

Sorry to hear about the developers. I’ve got very hard water in my area, so collecting rainwater is the way to go for me.

Barley straw is a safe and cost effective way to treat your water supply and rid it of algae. You place it in a net bag of some sort, I used bags I bought oranges in and place in water. Then, you leave it alone. It creates hydrogen peroxide and the algae dies slowly. It’s used in koi and goldfish ponds to treat algal blooms which are bad for fish. Algae grows quickly depletes the water of nutrients and then when it does and decays decreases oxygen. I used it in my fish pond for several years with no I’ll effect to my fish, plants or my BC that grew in there. The oxygen part in the water probably won’t bother your trees any but if the algae is growing in your pots it’s using up your fertilizer and will clog your pots. Then you will have a poor draining, hypoxic soil environment that could affect tour trees. Just my 2 cents.

Thank you for your input here!
That is really interesting, and something that is pretty easy (and safe?) to test out it seems.

Can you tell me a little more about how you go about this? I understand you keep it in a mesh net of sort, probably something plastic.

Is the barley fresh or dried? Do you buy it, or could I go and pick it up from any field (with permission of course)? Do you cram it together into a ball and stuff it in the net, or does it have to be intact? How much do you use (my two tanks are 300 liters ~66 gallons)? How long do you leave it in there - is it all the way to decomposition?

You can no them almost anywhere, can find them on amazon, pond supply and pet/fish stores too on occasion. They usually come already in a bundle, 1 usually is enough to treat 1-3000 gallons. I simply place in the water and leave it be, it will take aime time before it atarts working 1-2 weeks. Leave it in there for about 2-3 months and then replace. Home depot amd Lowe’s sells and extract that you would likely only use small quantities to effectively treat your algae problem. Maybe 5ml or a teaspoon once every 2-3 days at first and them periodically as needed.

Thank you, that might be just what I need!

How is your water supply doing? What method did you ultimately pursue?

Sorry for the delayed reply here. The winter and early spring has been really dry here, so I ended up emptying the barrels and cleaning them off with a light chlorine dilution, relying on the tap for watering for a while.

Since it has started raining again I’ve also been using the water more and haven’t had any problems so far. Basically I think the water was just left untouched in the barrel for too long last time.

I am considering getting a 1000L barrel, and when that happens I think I’m going to have to the barley way.