Jsoon,
I don't use brush. Instead I have been using white spongy filter material ( I call it soft Jap mat ) and change daily. It work wonderfully well - imagine I have 18 - 20 kois and 1 talapin, some guppies in my FB pond. The water parameter so far after two month experiment is very good, water clear and most importantly my kois are happy.
With this daily change of filter media of 5 min job [
the dirty filter media - about 2 - 3 or more depending on the need can then be soaked and washed as and when free - just flush with water ; but when the fibres are getting loose after washing for a few times, I will dispose it off - one pack of 5 - 6 media cost $2
]. I believe this way of handling filter can only work for small pond when the pond get bigger, the filter size needs to be bigger and changing out can be a nuisance - brush will be better. I think dttk or Johnson will agree with me as theirs are big ponds. I implement this out of no choice as I could not get the right type of brushes in the beginning . I do drain my filter tank bottom very often to ensure the overflow dirt at the bottom be cleared as this bottom slug may make the water a little unpleasant due to H2S and this is potentially hazard to the kois.This could be done within 5 min and the water of the bottom will be drained directly to the plant sorrounding it. I can feed my kois as much as I can without jeopardizing the quality of water ( in the event that I feel need, I just replace the filter )
. Besides, my main filter tank is about 12% of the pond size which save a lot of space and with a insignificantly small additional filter tank, the total filtering capacity is still less than 20% of the pond size. This is revolutional against the generally accepted 30% figure.
However, having said that, this is still in the stage of experimenting and only time will tell whether it is effective but so far so good.
I will post my filter through dttk for your reference as my pic sizes are too big for direct posting here. Thanks dttk
for giving u the trouble.
Cheers
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Filter Brushes
. I did mention brushes but I don't recall saying coconut brushes 
. Seriously, any type of brush will do as long as they are easy to clean, durable and arranged correctly. What the brushes are made of is not important as long as they're non-toxic. By the way, what do you mean by "yet to see the difference?" 
. have a great day! 
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