'Tis the season.....

[GaryD]

Hi,

Despite hundreds of words of explanation about shallow grow beds, newcomers to aquaponics can't help but be confused by the continuing misinformation on grow bed depth.

Found this post (http://www.aquaponics.net.au/forum/showpost.php?p=17163&postcount=18) on Practical Aquaponics.....


And obviously... a greater depth of media... equates to a greater surface area available for bacterial conversion....

OBO utilises this principle by cutting blue barrels in half vertically... and more recently by filling entire IBC's with media...

Conversely, and totally overlooked in the "huff and puff" of the mythconceptions arguement about growbed depth....

Shallower grow beds, while they will work for plant growth... have less surface area available... and I mean total media surface area.... and hence less filtration capacity....

To put it in a "nut shell".... your bacteria colony can only increase to the level of the available surface area of your media... assuming sufficient oxygen...

If you don't have enough filtration capacity... surface area... and a heavy feed load.... then you will ultimately overwealm the medias ability, even with worms.... to breakdown the solids being pumped into the filter... and ultimately deprive the availability of oxygen for the nitrification process...

This another reason why shallower grow beds... unless you add more of them to compensate.... are more likely to cause "blockages"... and become "septic"...
Now, while all of this seems logical enough, the devil's in the detail.....


And obviously... a greater depth of media... equates to a greater surface area available for bacterial conversion....
No, depth has nothing to do with......the volume of media is the key issue.


Conversely, and totally overlooked in the "huff and puff" of the mythconceptions arguement about growbed depth....

Shallower grow beds, while they will work for plant growth... have less surface area available... and I mean total media surface area.... and hence less filtration capacity....
No-one has ever disputed that, if you have half the media, you have half the nitrifying capacity. What I have said is that you can have twice the growing area in 150mm deep grow beds as you can with 300mm ones......for the same amount of media.

In any case, I always recommend the use of supplementary bio-filtration for reasons that I have detailed at length. That, and the inclusion of some basic mechanical filtration, will not only increase the productivity of the system but also make it a safer place for the fish.......and make the number and depth of grow beds almost irrelevant.

This nonsense ignores the fact that there are other ways (indeed much less expensive and much simpler ways) to provide bio-filtration than grow beds. Not only that, but you are no longer bound by arbitrary component ratios. You can simply add whatever growing system you want when you feel like it.


If you don't have enough filtration capacity... surface area... and a heavy feed load.... then you will ultimately overwealm the medias ability, even with worms.... to breakdown the solids being pumped into the filter... and ultimately deprive the availability of oxygen for the nitrification process...
And my point is, that if you don't allow the beds to fill up with sludge in the first place, then you can feed more, grow fish faster and in greater safety than if you do. It really is that simple.


This another reason why shallower grow beds... unless you add more of them to compensate.... are more likely to cause "blockages"... and become "septic"...
Far from become blocked or septic, the situation that I've described will be much cleaner than the basic flood and drain system......and it will work much better.....for very little additional cost.

With the utmost respect, Rupert......re-arranging words is no substitute for logic and rational thinking.

Gary

[Rew]

In Rupert's defense, when he said surface area I believe he was talking suface area of his media, not growing surface.

[GaryD]

Hi Rew,

Yes, I understood that.

When I responded to Rupert's observations about growing surface, it was to counter the implication that the automatic consequence of reducing the grow bed depth was to reduce the surface area of the media.

As I pointed out, that was not the only option (and certainly not one that I've ever recommended).

For a start, you could retain the overall volume of the media and have much more growing area.

Also, I have always argued in favour of supplementary bio-filtration.

I just reject the idea that adding more grow beds is the only way (or even the best way) to do it.

The simple and inescapable fact is that, if you are going to rely solely on grow beds for solids capture and nitrification, you are always going to need more of them......because, by filling them up with solids you've impaired their efficiency.

By adding some mechanical filtration (and some supplementary trickling bio-filtration), not only do you keep your existing beds much cleaner (and therefore much more effective as bio-filters) but the number of grow beds and their depth are no longer such critical issues.

Those who attach to the basic flood and drain model (particularly in Australia) know that it has some of the things that were originally claimed for it are illogical and, in some cases unsustainable, but they've been so rigorous in their defence of the model that it will take little time for them to acknowledge (publicly at least) that there are other (indeed better) ways of doing it.

Interestingly, relative newcomers to aquaponics seem to be grasping this message so, what we're seeing now, is an attempt to qualify some of the old rhetoric with words like "balance"......or to suggest that, if your basic flood and drain system is not working the way you were told it would, it must be because you have too many fish or that you were overfeeding.

As I've pointed out in other recent posts, some of the original rhetoric and prescriptions are being modified and qualified......and that's a good thing. Now, we just have to wait for those who make and sell aquaponics systems to catch up with the new reality.

Gary