Bio filter flow rates?

Questions about pumps, filters and all pond equipment.
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Bio filter flow rates?

Postby dawdle » Tue May 20, 2008 8:10 am

One of the changes I made to our pond that was ok and now is not was to change the pipe from the pump to filter as it was clear pvc and would get blocked with blanketweed. This did increase the flow rate through the filter quite a lot.

I checked the flow rate through our filter yesterday and it is 800lph. In our 450l pond that means the pump turns the pond over 42.5 times a day.

I messed around with the flow rate and after leaving it at 450lph for an hour or so I saw a big difference in the nitrate(Edit: Keep doing that should be nitrite.) level from the filter vs the pond. But at about half the flow it should be doing double the work? It's impossible for me to calculate if it would be more efficient at that rate as my tests are not accurate enough.

I realise there are so many variables but wondered if anyone had any experience with flow rates through filters and whether flow rates can make a difference to efficiency.

Last edited by dawdle on Tue May 20, 2008 4:01 pm, edited 1 time in total.

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Postby jpcwebb » Tue May 20, 2008 11:47 am

Residency in the filter is one aspect, but filter media surface area is also a big factor - you can get away with higher flow rates if you have the right kind of filter media (ideally with very high surface area), and the filter chamber is big enough. Temperature also plays a big part, so efficiency will vary from season to season and on a diurnal basis (night vs day) and depending on the weather. Also, you want to strike a balance between increased retention time in the filter and adequate turn over of the pond to process the waste and keep the water moving. The general rule of thumb is turn over the volume of the pond between 8 and 12 times a day. But as you say, there are so many variables that I think it really comes down to trial and error. I think you could nevertheless reduce it further (maybe split the flow from the pump to reduce strain on it). In the winter you may want to reduce it to a trickle otherwise you risk excessively chilling the water and losing the thermal stratification.
Last edited by jpcwebb on Tue May 20, 2008 11:50 am, edited 1 time in total.

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