About Ponds

How big a filter should I get?

There are many variables affecting the ratio of gallons per flow rate for every type of filter in use. . Water hardness, number of fish and their size, filter medium, cubic inches of filtering material, organic waste load, (how fast will it clog?) etc. But, relax…most filter manufactures have done the work for us recommending the pump or pond size for their products. If you follow their guidelines and the filter design is not flawed, they work fairly well.

Preferred Filter Design

Maybe I just got beat over the head too many times by Gregg Wittstock at his pond seminars but we really like the out of the pond, flow through type filters. preferably an up flow filter, acting as a waterfall. These contain some sot of filter media where bacteria colonizes and does the work of a biofilter.


Place your pump away from return to circulate the entire pond as best as possible

Gallons per hour

Be sure that your planned filter is able to process a least 2/3 of your pond volume per hour preferably the whole pond volume at least once per hr….more isn’t necessarily better.

If you are over pumping your filter, pushing it past the recommendation of the manufacturer, then that biological filtering effect has a hard time taking place. Unlike swimming pool filters that are designed to completely filter out anything that comes along, a pond filter needs time to trap things, let them biologically decompose and the beneficial stuff gets returned to the pond.

You want a Real Bio-Filter

There are many filters out there that fall far short of what a biological filter should be. A biological filter provides what is needed for the biological filtering process; oxygen, bacteria and time. If a filter sets down in the pond, the only way for it to get oxygen is from the water. Any filter in a box designed to be set in the bottom of the pond, is therefore not a biological filter. These are fine for keeping a fountain running clean or for aeration. If the filter is nothing more than a container where a pump has been placed wrapped in filter media this is not a great design and far from being a biological filter. In a short time the outer layers of the media will clog and then the water is being simply pumped around the media and through the pump with not much biofiltration happening at all. Also, cleaning this type of filter is more work. You have to pull it out of the pond, which dumps about half the stuff it trapped right back into the water. Other big problem with this “wrapped pump” design is that it causes the pump to heat up often causing early failure.

Small square box filters which set out side the pond are getting closer to the right design, but most often they are far to undersized to do the job.

Biological Filters:

Decay is the key word when talking about the biological filtering process. Think of it as the life cycle of the pond. Plants and animal life die and bacteria begin to decay the matter in stages. Ammonia is formed, then nitrites, then nitrates and finally nitrogen. Nitrogen is basically plant food. As things die and the process completes its cycle the resulting effect is a nutrient for plant life. The plant life is eaten by animal life etc. cue Elton John’s Circle of Life.

A couple of points: Ammonia is deadly for fish and other living things. Algae thrive on nitrogen. We want our biofilter to get rid of the ammonia and also feed on the nitrogen to such an extent that the algae is starved out.

Higher forms of plant life in the pond and around the pond will help keep the algae growth under control by taking away the available nitrogen and by also shading the pond.

Do not over clean your pond and filter The biological process takes time, if you hurry it up by cleaning, you most often also remove the beneficial bacteria colony and/or nitrogen consuming algae… more will grow and very quickly. . With the right filter the pond should take care of itself. Start it up in the spring by spiking with some beneficial bacteria, let it run all summer and only clean it at the end of the season.

Do not over feed your fish: Uneaten food becomes waste. Excess waste matter in the pond in any form adds more ammonia which is detrimental to both animal life and plant life. Excess ammonia levels in the pond and filter will slow the natural cycle down and produce more algae. Fish are natural algae munchers, but are also lazy for the most part. If you feed them too much from outside the pond they will simply stop eating the algae in the pond.

Reduced Sodium Diet

If salt slows the growth of algae it has got to slow the growth of the other plant life in the pond, it is almost impossible to gauge the right amount of salt to add to a pond (if there is a right amount) which will slow the algae growth and still let the other forms of plant life survive.

If you want to treat a sick fish with salt then use a sick tank. Keep salt out of your pond.

What about the fish in winter?

For fish to live in a pond the water must be deep enough for the fish to have room under the ice to survive. We suggest that you will need to have a spot in your pond that is at least 24″ deep (30″ is best) and wide enough to hold the number of fish you plan to winter over. Also a deicer and a small recirculating pump or bubbier are a must. Koi and goldfish can handle the cold, but even when they go dormant for the winter their natural bodily functions continue. A by-product of this process is ammonia and other harmful gases. The deicer keeps “a hole” open in the ice for these gases to escape.

Snails, tadpoles, frogs, turtles and such… These guys are neat and fun to watch. In the wild they have their place in the grand scale of things, but in a pond environment they really are just a novelty

Snails and tadpoles do eat algae to some extent, but it would take a bunch to have any real effect on algae control in the average pond.


One of the products available on the market under a variety of names is an “algae clumper” or water clarifier. This product claims to clear up cloudy water or green water by making the suspended algae in the pond come together forming a mass which is heavier than normal and therefore the “clumped” algae sinks to the bottom clearing the water.

The clumper i.e. clarifier additive clears the water, but the cause of the over abundance of algae is still there. As a matter of fact if you keep using this product you set up a cycle that actually promotes algae growth. By taking out the old algae you create a perfect environment for new algae to grow, which triggers a cycle of clearing the algae, grow new algae, clear it and so on. There is nothing wrong with these types of additives and in fact we sell them, we just recommend that you use them sparingly. They can be very helpful in the quest to cure the actual problem.

In this example, what one might consider, is to go ahead and clear the pond, but also re-establish a beneficial bacteria colony which is large enough to eat the algae or else add a few more aquatic plants to starve out the algae.

Some Pond Tips

For ease of cleaning and maintenance an out of pond filter system is best.
Use surface skimmers either floating or shore mounted
Go larger than you want for first pond. Trust me; people nearly always regret not making it a little bigger.
Do not overstock with fish
Install an automatic fill valve
Call local water authorities for water qualities data and consider treatment of a filling pond
Plan where to route cables and conduits and plumbing
Never use a power source around any water that is not connected to a tested G.F.C.I. circuit
Don’t overfeed fish
Aim for a surface coverage of plants of 60% or more
Ponds can hold fish far beyond what is normally recommended if the filtration system is built to take that size of bio load and is maintained regularly
Read about the biological processes that take place in a pond until you understand the relationships completely