How to choose a pond filter

When it comes to choosing a pond filter for your pond, you want to consider the amount of fish your pond is housing and its overall size. Since many filters on the market are made for ponds with minimal fish, you could easily buy the wrong size for your needs. This is why I recommend starting with finding the size of your fish pond first.

Calculating Your Pond’s Size

If you have yet to build your pond and want to know exactly how many gallons your pond is and should happen to have a water meter on your house, then you’ll love this. Write the number on your water meter down and then go and fill your pond up. When your pond is filled up, go back to the water meter and write the number down again. Now subtract the first number from the second number, and that is how many gallons your pond is!

For those of you who already have your pond filled, I suggest doing the following: (LENGTH’ x WIDTH’ x AVERAGE DEPTH’) X 7.48

It is essential to use your average depth, and not the deepest point as that will give you more gallons than you have. I also suggest taking 15% off of this figure to get an even better idea of how many gallons your pond is.

How Many Fish Do You Have?

Now that you know how many gallons your pond is, the next step is to figure out your pond’s fish population. The standard rule of thumb is to add one inch of adult fish to every five gallons of pond water. For example, let’s say you buy some comets for your pond; they will reach an adult size of 12 to 14 inches in length. So, you will want to provide about 70 gallons of water for just one comet. Now, let’s say your pond is 1000 gallons in size. I would say 14 to 15 adult comets would be fine for your pond, and any pond filter that’s rated for a 1000 gallon pond will do. If you decide to have 40 adult comets in your 1000 gallon pond, then you will need a much bigger pond filter, probably something rated for a 3000-gallon pond will work well.

I like to think of pond filters as a septic system for the fish in your pond. Make sure you choose a filter that offers a lot of biological surface area. The bacteria that grow in this area will gradually feed on fish’s organic waste and break it down naturally. Just like a septic system, you will also need to use a biological additive that will help aid the filter with the breakdown of waste. Common bacteria additives that are sold on the market are Microbe Lift PL or BioSafe’s Xtreme.

Do I Need A UV Filter?

Should I buy a pond filter with built-in UV or pond Filter without UV? This is a question that I get asked a lot. If you have a balanced pond with 50% pond plant coverage, you won’t need a UV light filter, since the pond plants will work in controlling the nutrients that cause green water. If your pond is going to have very little pond plant coverage, then you really want to consider a filter with a UV. UV sterilizers can be tricky, and it’s important to have the proper one sized up for your pond. I see a lot of manufacturers that inflate their UV’s abilities, and it can be really frustrating at times as to why they do this. The two important things to keep in mind is, (1) matching the right wattage up to the amount of water you are going to treat and (2) providing the proper flow rate through the UV. My favorite UV manufacturer is Emperor Aquatics UVs since they use EPA guidelines to come up with their flow rates. That’s how they can make a clear water claim in 3 days. I wish everyone followed this as it would make things so much easier.

Choosing A Pond Filter

Once you’ve narrowed down your choices above, it’s time to pick out your new filter.

For a standard size fish pond between 1,000 – 2,000 gallons, I recommend our Aquascape Ultraklean pond filters. These biological pressure filters come with an integrated UV clarifier that can be programmed with a timer. These are perfect for minimal maintenance builds.

The best set up that I can recommend on ponds up to 5000+ gallons in size would be one of our Professional Filters hooked up to an Emperor Aquatic’s Smart UV Sterilizer. This set up would require the least amount of maintenance and would last for many years.

No matter what pond filter you decide to run with, AZ Ponds has a large product selection with everything you need, with free shipping options available.

This doesn’t answer your question? email us at