Keeping a pond clear
June 30, 2019 7:07 AM   Subscribe

What can I do to minimize algae growth in a pond?

We have a small pond in the front yard of our new house. We moved in last month and have been trying to do some research as this is all new to us. The first few weeks after moving were pretty busy, and we didn't pay much attention to it. We finally had the time to drain the water and clean it all out, and it looked really nice for a while. We started adding algaecide weekly per the internet's suggestion, but now 2 weeks later there is a green film at the bottom.

Here is the pond immediately after cleaning. This is what it looks like today.

It does get a lot of sun during the day. Should we add plants? I don't want to add fish, if I can.

Any help would be greatly appreciated.
posted by cozenedindigo to Home & Garden (17 answers total) 2 users marked this as a favorite
A little of that is probably normal. Floating plants will certainly help a bit as they spread and cover the surface. The go-tos for this sort of things are water lettuce and water hyacinth.

You could also do water lillies (which need a lot of sun) or lotus, and maybe a marginal plant or two (horse tails are nice) in submerged pots. Your local nurseries should be able to point you towards the right stuff for your area (as well as what's considered invasive/verboten). Without fish, you're likely to attract interesting insects - damselflies and similar, and marginals will give them a nice place to perch. I love raised ponds, kept a simple one on a deck years ago, and would love to start one again when I have some time.
posted by jquinby at 7:33 AM on June 30 [1 favorite]

Plants have really helped keep our backyard pond clean. I don’t even have to use any algaecides or pond cleaners anymore! Floaters (water hyacinth, water lettuce) seem to be especially effective - in addition to thriving off the nutrients, they cover part of the surface and provide shade. I also have a hardy water lily, a lotus, and some marginal plants.

Also, a circulating water pump of some kind helps keep it clean. We’ve got a simple fountain with a filter attached to the pump.
posted by chemicalsyntheticist at 8:16 AM on June 30 [1 favorite]

Seconding that some of this is probably normal. Maybe reconsider the fish? They do give a nice touch to ponds like these and there are also varieties you can get that eat algae. Mainly, though, I think of some algae as the start to a normal pond environment. I wouldn't worry about it as long as it doesn't get out of hand. Finally: maintaining running water is crucial towards keeping algae levels down.
posted by Armed Only With Hubris at 8:20 AM on June 30 [1 favorite]

Forgot to mention: there is a fountain that maintains running water constantly. I will look into the plants though!
posted by cozenedindigo at 8:40 AM on June 30

Also, just from poking around online, I see it is possible to pump water through a UV filter to prevent algae accumulation.
posted by Armed Only With Hubris at 9:08 AM on June 30

Are you in an area where you’ll have to drain the pond for the winter?
posted by sciencegeek at 9:37 AM on June 30

Yes, we'll be draining it in winter and bringing the pump etc inside the house.
posted by cozenedindigo at 10:37 AM on June 30

If you don't want fish, a few low-maintenance snails might do the trick.
posted by Rust Moranis at 10:47 AM on June 30 [1 favorite]

I'm an aquatic ecologist. Do you fertilize your yard? Stop. That will help to some extent (it will also help everything downstream of you in your watershed, too).

The suggestions above about either having plants on the surface of the water or algae feeders in the water are good. Fish and snails are both great choices--in either case, make sure that they are confined to your pond and don't dump them in local bodies of water when you're done with them.

Otherwise, you can keep dumping poison in, if you want, but I'm not sure I see the point.
posted by hydropsyche at 10:54 AM on June 30 [5 favorites]

I’m a plant ecologist. Water hyacinth is a nasty invasive species around the world; please don’t use it unless you live in the Amazon.
posted by SaltySalticid at 11:40 AM on June 30 [8 favorites]

Sorry, yes, I should have said don't release your plants into the wild, either.
posted by hydropsyche at 11:50 AM on June 30

I’ve heard good things about Microbelift but haven’t used it myself.

For plants you’ll have a choice between buying locally and online - online retailers, at least the ones I’ve used, tend to be pretty clear on what species they won’t ship to your state. Water hyacinths are on most restricted lists.

There are some quite pretty native aquatic plants that you can choose from. Do a little research and get something fun.
posted by sciencegeek at 12:50 PM on June 30 [1 favorite]

A waterfall or fountain of some kind will aerate the water. Oxygen will keep the algae down to some extent. Same principle as in a fish tank. The bubbler mixes the water up with oxygen. That's my theory, at least.
posted by diode at 3:09 PM on June 30

If you want to keep it with nothing living in it, you can chlorinate it like a pool.
posted by Gneisskate at 6:59 PM on June 30 [1 favorite]

Algae consume oxygen at night, like all plants do during respiration. Aeration won't do anything to prevent algae, in other words. The best way to minimize algae is to: 1) keep nutrients out of the pond by making sure there is no runoff from your lawn; 2) add plants to use up nutrients; 3) shade the water. Water lilies for small ponds or frogbit are good for this because they do the second and third thing at the same time.
posted by oneirodynia at 9:52 PM on July 1

Ah, forgot to mention - submerged plants can also help use up nutrients. Anacharis works really well for this but will need to be pruned back occasionally. Again, you'll want to check with a local supplier or nursery.
posted by jquinby at 5:34 AM on July 2

The solution seems to be to treat it like a pool, and just throw a chlorine puck in the bottom. Still clear! Thanks everyone.
posted by cozenedindigo at 9:11 PM on July 6

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