Goldfish Pond Filter

by Robert Waters
(Chicago, IL USA)

Hello,

I'm doing research on a 250 gallon indoor goldfish pond set up and had a question about what filter to purchase.
I am trying to decide between the Laguna Pressure-Flo 700 UVC Filter or the Laguna Pressure-Flo 1400 UVC Filter.
I am thinking the 1400 might be unnecessarily powerful but worry about not having the biological filtration if I purchase the 700 model.

If you could help guide me I would greatly appreciate it!

---

Grant's Reply


Hi Robert

I tend to agree with your comment that the Laguna Pressure-Flo 1400 UVC Filter might be unnecessarily powerful.

Goldfish live in still or slow moving water. They aren't that happy in fast flowing water, especially the fancy twin tail varieties.

The Pressure-Flo 1400 filter is rated for a 1400 US gal pond with a maximum flow rate of 1400 gallons per hour. This gives you a water turn over of once an hour for a 1400 gallon pond.

Under low biological load the smaller 700 filter will have a flow rate of 660 gallons an hour which will give your pond a turn over of 2.5 times an hour. That is the amount of turnover you would need for a crowded aquarium.

Ponds with a low bio load can have a turn over as low as once every two hours, so in your case a filter with an output of 125 gallons an hour would theoretically be enough.

If your biological load isn't going to be high, and you mention the pond is indoors, the Laguna Pressure-Flo 700 UVC Filter which is rated for a 700 US gallon pond will easily handle a 250 gallon pond.

That is the biological filtration sorted, now you have to consider the UV clarifier.

UV clarifiers/sterilizers become less efficient the faster the water flows past the UV lamp.

If your pond was in full sunlight and had a high bio load, the maximum water flow Laguna recommend is 330 gallons per hour. This sounds counter productive for the filtering process, which it is, but a high bio load promotes lots of algae. To kill it effectively, you have to slow down the water flow.

At 330 gph you would still achieve a water turn over of 1.3 times an hour which would be adequate.

I would purchase a water pump with an output of around 500 gph which is a good compromise between good biological filtration and UV clarification.

If you are thinking of installing a fountain or waterfall, you will need to go bigger in pump size to allow for water head height etc.

I notice Amazon are selling Laguna Pressure-Flo 700 UVC filters at competitive prices at the moment.

Regards

Grant