Do I Need to Change My Fish Pond Filter?

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This was a question I received recently....

Hello Tony, I have been receiving your articles for some time and find them very interesting and informative.

Even though I have had a pond for about 20 years I still feel I there is more to learn.

About 5 years ago I put in a new pond about 4000 U.S. Gallons - my fish needed a bigger home. Yes, I have had some for as long as 20 years. I used my original outside box filter (approx. 18inches wide x24 inches long by 24 inches tall) installing it at the top of a hill to create a stream and a waterfall. The filter has 3 filter pads on top and about 5 inches of short tubes on the bottom.


The water comes in at the top on one end of the box and spills out the bottom on the other end. I also have a skimmer at the low end of the pond in which sits the pump that pumps the water to the top of the hill and through the box filter.

I have good pressure and the waterfall (about 18 inches above the pond) creates a good agitation. When I first set up this new pond I did not have much mantainenance, however last summer I had to change the filter pad in the skimmer at least once a day and clean the filter pads in the box filter about once every two weeks. If I didn't the box filter would overflow it became so clogged.

For fish I have about 10 very large butterfly koi (approx. 17") two smaller (approx. 10") and about 6 small (approx. 5"0). I do feed the fish a small amount twice a day and do use Pondzyme. After the first few weeks the water is very clear and the ph and nitrate levels a good. I check at least once a week.

Another important piece of information - I live in the North East of the U.S. - Right now I miss my fish very much. I would like your input on what I can do to improve the filter system without a major renovation on the pond. Can I add new materials to the box filter? Do I need a new filter? Are the new pressure filters the way to go? Thanking you in advance for your input.

Lois Athanasiou  

My reply...

Lois, Thanks for the email.
Based upon what you tell me you have no need to replace the filter

I suggest you might consider adding some powerfil biomedia (copy and paste the following link into your browser to learn more) to increase the biological capacity of the filter (see below)

To avoid the hassles of cleaning the mats I suggest remove them and see what happens... the media referred to above will compensate for any lost biological surface. I'm pretty sure that it was algae clogging your mat