bio-filter construction advice

[digitalmikeon]

Hello everyone, just new to this forum, first post! I do not have a fish pond but I have constructed a tank set up for a soon to be very large snapping turtle named "Darwin". His new pond is made from a 150 gallon plastic stock tank 2'x2'x6' running through a 35 gallon upflow bio-filter, all diy. Now my question is this... I have an air pump and air stones to use in this system and I would like to use them in my bio-filter as opposed to being in the stock tank with Darwin, (he tears apart everything that is not made out of stone or solid concrete pretty much). Will having air at the bottom of my filter in any way impede its ability to work properly. any advice which you might like to present would be greatly appreciated. Thanks in advance

 

[koiguy1969]

adding oxygen is always beneficial to a bio filter...the more oxygen rich the water the healthier the aerobic bacteria.

 

[addy1]

Welcome to the group! watch your fingers lol

 

[digitalmikeon]

Thanks, I suspected that was the the case but I wanted to hear it from someone in the know! One more question regarding water flow through this filter is going to rather quick, does the speed through the filter and back into the tank hurt the bio-filtration process. I do not think that it would, but one never knows when dealing with new things.

 

[addy1]

A one hour turn over is a good rate, but faster does not hurt it. Some ponds turn over in 1/2 hour
How big is your pump for the turtle tank?

 

[digitalmikeon]

pondmaster 1800 gallon per hour!

 

[addy1]

So 350 gallons into 1800 = 12 times an hour.

Turnover - The quicker the better?

Just when everything starts to make sense, along comes a complication. While a longer filter retention time will produce better water quality we also have to consider pond turnover times. Why? Because polluted water is produced in the pond and, if there was a slow turnover at the filter, it would take longer for pond water to get processed by the filter.

 

[addy1]

more info!

How do you calculate the retention time of your filter? Doing the Maths

This is determined by the flow rate and the volume of water in the filter. If water output from the filter is 2,000 gallons/hour and the filter contains 500 gallons (when full of media) of water then:

filter retention time = filter size / pump rate

so, in our example:

retention time = 500 (gallons) / 2000 (gallons per hour flow rate) = 0.25 hours (which is 15 minutes).

So a given sample of water will take 15 minutes to pass through the filter and back to the pond.

In the above, the filter capacity represents the amount of water in the filter - not the physical size of the filter, which will be greater.

The retention time and the size of the filter will depend to a very large extent on the type of filtration medium used.

A solid medium with low void space such as gravel will occupy much more filter space than large-pored, lightly packed media and therefore leads to a lower retention time.

More calculations!

Using our same example of a 500-gallon filter. If we now nearly fill it with gravel, the volume of water it will hold will be reduced substantially - maybe to as little as 150 to 200 gallons. Using the above example, the retention time of such a filter would now become;

200/2000 = 0.1 hours (6 minutes) or less

In comparison, if the same filter was filled instead with matting or plastic, there would be hardly any displacement and the filter will probably still hold in excess of 450 gallons, giving a retention time over double that of gravel. So a filter with a dense, low-void medium, such as gravel, will need to be substantially larger than one based on light-weight media, in order to achieve the same retention time, which explains why koi filters were traditionally so large.