How to Keep You Pond Water Crystal Clear and Healthy

There are two areas that need to be addresses in order to maintain consistently clear water in your garden ponds they are sufficient filtration and controlling algae.

Sufficient Filtration and Reasonable Fish Load

The best way to ensure your pond water will stay clear and free of algae is to have a sufficient filtration system in place and to keep your fish load light.  The choices of filters available to you is almost endless.  If you are handy you might want to make a homemade system like I did or you might want to avoid the hassle and buy yourself a filter system that is ready to go.  Either way is fine just as long as the filter system is sized for your pond.  The best advice I can give is to oversize the filter system by at least 20% and talk to as many local pond 'experts' as you can before you begin.  By expert I mean people like you who have ponds in their backyards, not the guy at the local nursery who wants to sell you a basic pond starter kit. 

Another thing about filtration, unless your pond is a very small preformed unit avoid the filters with an in-the-pond pump.  You will forever be cleaning out the thing, a truly unpleasant job.  The filter I built in my step-by-step pond building section of this website is an out of the pond system that filters the water before it gets to the pump eliminating a whole bunch of maintenance time.  (If you must use the in-the-pond pump set up take a look here)

Every new pond will suffer from many water quality problems until the biological part of the filter system has a chance to establish itself.  Do not get discouraged, your pond will come around if you have all the components of a good filtration system in place.  These include a mechanical filter that removes solids from the water, a biological filter that will convert ammonia into nitrates, and a vegetable filter that pulls the free nitrates out of the water. 

Here's a tip for the new pond owner: Ask one of your local pond experts to lend you a fresh dirty filter pad.  Rinse this out right in the middle of your pond.  Sure it will cloud the water for a few minutes but it will also introduce a ton of great bacteria into you ponds ecosystem. It really works!

Controlling Algae:

Aquatic Plants, Ultraviolet Clarifiers and Barley Straw

The biggest enemy of clear pond water is algae.  Algae blooms can really fowl up a pond quickly.  Having a method or system for controlling the algae before it starts is very important.  First you need to understand how it grows before you can diagnose and cure the cause. 

Biological filters turn ammonia into nitrate which in turn feeds algae creating an algae bloom. There are two types of algae problems, pea-green water and blanket weed. During the hot summer months excessive algae will use up most of the oxygen leaving the fish gasping for air at the surface.

There are various ways to get rid of the algae; using a vegetative filter (living plants), an ultraviolet clarifier  (will not kill blanket weed), algaecide chemicals, magnets placed on the filter pipe (never worked for me), and barley straw (least expensive and most effective).

Vegetative Filter

A vegetative, or vegetable, filter is basically a shallow tub, pond, or free surface area of a filter that is populated with living plants.  The plants will use the available nitrate (produced by the biological filter bacteria) so it is not available for the algae.  Pretty much any water plant will do such as rushes, miniature cattails and seaweeds.  I, personally, have had the most success with floating plants such as water hyacinths, water lettuce, and duckweed. Just be careful which plants you choose, I live in Eastern Pennsylvania where water hyacinths are not invasive.

For more information click

	The Pond Doc's: Vegetable Filter: The Whole Story
	Springfield Watergarden Society's Watergardening 101: Veggie Filters...

Ultraviolet Clarifier

An ultraviolet clarifier kills suspended algae as it passes the light source. The ultraviolet clarifier, in general, does not eliminate string algae, but is very successful at eliminating pea-green water, especially in ponds where the water garden is insufficiently planted. An ultraviolet light is not a substitute for mechanical and biological filtration.

Fortunately I do not need to use ultraviolet clarifiers year round, usually it will be run for the first few months of spring until the natural biological system of the pond can keep pea-green algae under control.  I have also found ultraviolet clarifiers to be very effective year round in several of my friends smaller ponds that are situated in a full sun setting. 

Algaecides kill pea-green water and string algae but they can also kill pond plants and snails. I recommend avoiding this harsh chemical if at all possible, unless all other algae control methods do not seem to be working. Just remember it will be a very short term fix. For about the same cost and duration of effectiveness try a bottle of pond clarifier.  It is nontoxic and it will clump all the algae together so your filter can suck it up.

Magnets

Magnets can be used on filter return lines to control pea-green algae (does not work on string algae) but can require special procedures, such as reversing the magnets every year. I have found them to be totally useless in my ponds but they may work for you.  I'd love to hear from you if you have had success.

Barley straw has been used since the middle ages to keep ponds free of algae.  Putting a small bag of it in your pond each spring will reduce the amount and duration of both 'pea green' and string algae.  As the barley straw starts to decay in your pond it releases lignin which acts on both single cell and string algae killing it. Once the straw starts decomposing  a reduction of algae becomes evident. The process continues for about three months so staggering the introduction of new barley is essential.  Ideally it ought to be placed near running water to maximize it's effectiveness.  I place a good heaping handful in an old onion or flower bulb net and hang it on the inside of my filter boxes.  It really works wonderfully!

Click here for a very detailed explanation on how barley straw works.

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Last updated on: March 29, 2005