Cheap media for bio-filter

[Kobus Jooste]

We have been discussing the options of adding smaller bio-filters to our units as mineralization sites, but not extra planting space as a result of the placement of the units (such as under a grow bed).  I have placed a sump tank made out of a washed 200 liter water barrel underneat one of my grow beds, and after seeing the fines settle out in it, decised to retrofit it as a bio-filter.  Due to the shape and difficulty to access this barrel, I have given up on trying to compartmentalize it.  I am simply going to put as much of my cheap floating net balls into it as possible, and add a small water pump to the sump that will draw "clear" water out of the sump and into my small raft and NFT array.

 

I'm following Sahib's example of putting the water pump into a filter box to ensure that it does not suck up loose fines (or as little as possible) from the sump.  The remaining task therefore is on filling the sump up with some kind of cheap, light media that can easily be removed and rinsed should the set-up start getting anoxic.

 

The water flow, although passive through the two 63 mm pipes, sets up a circular motion in the sump.  Not sure if this will remain if it is packed with net balls.  For the filter media, I have settled on something really cheap and easy to make yourself.  It does not have massive surface area - around 140 m2 per m3 by my estimations (half of gravel), as it is sparse fine netting.  The advantage is that it can trap solids many times its original weight, which makes it an ideal fines trap.  At around 8 kg for a cubic meter of the stuff, it is also easy to handle and clean.

 

 

The material I use is sold in bulk locally as onion bags.  A role like the one pictured above (I have made over a 100 balls from it already) will set you back around $6 and you can get around 250 net balls out of it.  What I do is cut a meter section of net, roll it into a ball and crunch it down.  It ends up looking something like a plastic pot scourer.

 

 

It takes about 2 minutes to make one ball, so it is not too much of a slog to make the 300 odd I need to stock the sump with.  What I still need to do is get the pump and make the basket for it - there I want to use the same sponge material that is used in aquarium powerheads.

 

This is a relatively simple set-up, but with two of these added to my system under the elevated gravel beds, I would have added the equivalent of one of my grow beds in mineralization surface area designed specifically (I hope) to deal with the fines that make it through the gravel beds.

[Sahib Punjabi]

Good example of thinking "outside the box"...great. Well done and thanks for sharing :-)

[Kobus Jooste]

Only a pleasure.  Hopefully this will get most of the fines trapped and give me clearer water and more nutrients.  I'm going to feed a raft bed and NFT out of the sump, which should free up enough capacity from the main pump to add six trickle towers to the system.  Once those are in, I think I have all the grow space inside the greenhouse covered.

Sahib Punjabi said:

Good example of thinking "outside the box"...great. Well done and thanks for sharing :-)

[Christian James]

Great idea!

[Harold Sukhbir]

Really great addition to facilitate your raft/NFT and AKA biofilter. I've set up a large enough swirl filter and getting about 80% fines filtered out. I like the onion bag idea but it's unavailable here. We have a couple PVC manufacturing factories that discard some thin "stringy" pvc continuous thread in huge balls, so I'm thinking of putting some in the swirl at the right density to allow water to flow through and trap the fines, and it will cost me 20 min shuttle.