Backyard Aquaponics
A place to discuss aquaponics

Hydroton is a brand name product made in Germany.... definitely not "chinese"... rest easy...

thanks for that Rupert!

Uhm... so I fear wading into this especially since I haven't been around for a while, but isn't the problem with aeoration made negligable if using ebb & flow? The water drains out through the bottom, air fills in behind it, water picks up the oxygen on the refill... isn't this correct? I mean, I can understand small pockets of anaerobic areas but that would be do to a low or problem area in the bin. Where am I missing it?

Tony

You're essentially correct Tony... and that's the beauty of flood & drain...

The arguement was more about media depth and equivalence of bio-filtration... and/or continuous flow...

In both cases... it has been shown over time that thin media depth growbeds, small media and/or continuous flow (slow flow) ... media and methods... result in clogging of the growbeds...

This is what ultimately/potentially leads to the formation of anaerobic zones in the growbeds...

If grow beds are not very deep, keeping siphons working over time can be tricky as the beds get more solids and roots in them and the flow through them is impeded. Since a shallower bed has less depth to work with for flood and drain, any loss of that flood and drain depth due to siphons sucking air too early can reduce the effectiveness of the flood and drain a bit.

This doesn't mean it won't work, just that the tolerances are closer so can pose more of a challenge.

And if a system is over stocked/overfed for the amount of media it has, beds can get overloaded with solids which like muck, don't draw in much air when drained and therefore can become anaerobic.

The vary nature of flood and drain does help deal with the aeration of the media but if not properly designed, even flood and drain can't solve all problems.

The question is not of surface area vs depth of growbeds but the total volume of media times the amount of aeration. You can go very deep on media, if you have a method of aerating the media. Barrels full of media work fine for biological filters if the column is aerated. In fact are often used in aquaculture systems.

This subject has been an interesting read and the views from different people about beneficial bacteria in a fish system varies a fair bit.
Media in a fish tank filter is generally measured in the amount of liters of media.The type of media used will give you an idea of how good the filtration will work for converting/removing toxins from the water.
A media like gravel is quite useless in a smaller filter to say something like scorio or matrix but thats not to say gravel will not add some beneficial bacteria to the system because it does but only in very small quantities.
Bacteria volume is also very dependent on water temp,aeration and most importantly the PH level.
Any water less that 7.0 PH struggles to keep bacteria alive therefore a large amount of media/surface area is needed compared to water with a PH higher than 7.0.
The higher the PH the more beneficial bacteria will grow and survive in the same volume of media.
A media that is porous (volcanic rock,matrix,coral,clay balls ect) will hold possibly hundreds more times the bacteria of a solid object like gravel therefore a small amount of media will be far more efficient than a huge amount of gravel.
There are 3 main types of bacteria that can be present in a fish system.
Two of these are what we strive for and must have and these are nitrosomonas for converting ammonia into nitrites.
Once nitrites begin to show up another bacteria called nitrobacter begins to grow and populate the media as the nitrite levels increase.These nitrobacter convert the nitrites into nitrates.
The 3rd bacteria that then can become present is the anaerobic bacteria which are caused from dead areas within the filtration system or fish tanks.These bacteria must have no oxygen to survive where as the first 2 are very dependent on oxygen levels.
Anaerobic bacteria can be very beneficial to a filtration system if managed properly and this is usually done in a separate chamber within the filter to convert nitrates into harmless nitrogen gas that escapes through the water surface providing there is agitation and rippling of the water surface.
As good as they can be they can also be a disaster to the fish system as they are very toxic if disturbed and can kill fish just about instantly if released back into the water column.
Opening up these pockets releases toxic substances like hydrogen sulfide.
Like you guys are all doing here plants and water changes are the safest way to remove nitrates.
Towers work far more efficiently than permanently flooded media but flooded is not far behind if aerated properly.That being said towers can be harder to maintain the water flow over the media as you more often than not get lots of dry area as there is no way to control the direction of falling water.
Most aquarium keepers that use towers always use flooded media as well as a backup.
As an example of media capacity for filtering water to convert the toxins to a safe environment for fish I have about 70 tanks choccus with cichlids and catfish. The bio load from the intense stocking levels is just massive and even after huge water changes twice a week my nitrates still run at around 60 to 80 ppm.
The amount of media needed for the nitrification process that I use is 30kg of 15mm scorio rock and 20kg of 25mm coral bones permanently submerged in my sumps so the water has to flow through the media baskets to reach the grundfos pump.
A plastic crate above the sump filled with filter wool and 2 grades of filter foam filters all the solids first and then falls through the bottom of the crate and into the sump to pass through the bio media and then on to the return pump.
If i was using gravel I would probably need 1 or 2 hundred kg's of gravel to obtain the same surface area of bacteria to fully convert the level of toxins produced in my system.
An example of my stocking densities here in my tanks.




So to really get an answer to the question of surface area vs depth of media when it comes to filtration of the water itself it all comes down the the media types used and PH levels but in any type of media used the more the better.You can never have too much but you can certainly not have enough.
At the end of the day if your water has 0 ammonia and nitrites you have enough media no matter how it is being used.
Your next question then becomes,,,do I have enough plants to remove the nitrates to at least a safe level for the fish to happily survive?
If not then weekly water changes come into play.

Here's a scientific example of the benefits of using a porous media (Matrix) compared to a solid media (plastic bio-balls)
Scorio has a very similar surface area for bacteria growth to Matrix.

Matrix™ is a high porosity bio media that provides efficient bio filtration for the removal of nitrogenous waste. Matrix™ is a porous inorganic solid about 10 mm in diameter. Each liter of Matrix™ provides as much surface (>~700 m2) as 170 liters of plastic balls! Plastic bio-materials provide only external surface area, whereas Matrix™ provides both external and internal macro porous surface area. These macro pores are ideally sized for the support of nitrifying and denitrifying bacteria. This allows Matrix™, unlike other forms of bio media, to remove nitrate along with ammonia and nitrite, simultaneously and in the same filter.

Bacteria colonies on the internal and external surface area of Matrix™

Thanks for the interesting and thoughtful analysis. Nice looking fish, too. And, obviously you have a lot of experience in not-killing fish, a very important skill many of us still are reaching for.

However, in practice, I've found having enough plants to remove nitrates requires enough gravel to handle the ammonia>nitrite>nitrate conversion quite easily.
I also prefer to have media smooth enough that carrots and other root crops can grow well and so it shakes from the roots of plants I pull out.

Hydroton may not have the porosity of the mentioned media... but the media itself is by the manufacturing method... almost "pop-corned".... containing a myriad of microscopic holes... increasing surface area for bacterial bio-filtration...

And I agree with hydrophilia.... if you haven't got enough bio-filtration capacity to deal with your ammonia and feed load... then all the plants in the world wont help you...

Conversely... if you have then there's more than enough plant growing capacity to deal with nitrate levels...

And nitrates just aren't a concern with freshwater fish... until they exceed levels of 400+...

not entirely true. many aquatic plants take up ammonia directly (http://www.aquabotanic.com/plants_and_b ... ration.htm). so in theory, aquatic plants as part of the filtration will do just as much for removing ammonia as biological (bacterial) filtration.

of course, we are trying to grow eating plants, which mostly prefer nitrates, so more growbeds that can make nitrate is better for us. but its not the only only option.

Duckweed can be a huge ammonia sink. However I haven't figured a good way to utilize it without having nasty gunk problems in the duckweed bed. How to remove the solids (in a fashion that doesn't require daily or even weekly filter cleaning/purging) yet leave the ammonia to glow into the duckweed bed. I have let straight fish tank water flow into a bed to grow duckweed and it did indeed grow duckweed but is also built up a dangerous layer of gunk which would breed those anaerobic bacteria and any disturbance could release hydrogen sulfide into the system so cleaning out the gunk becomes a problem.

I'm still trying to work out how to add a water plant portion to my system without having the gunk problems. I know ornamental ponds can be nicely balanced and do fine but how to incorporate that with a heavily stocked AP system becomes and issue since the most ammonia rich water is also going to be the unfiltered water which would totally foul the pond plant tank. Any idea which water plants would be most likely to take up ammonia or nitrate equally easily?

I always thought that a swirl filter would be the best option to remove solids. then all you have to do is open a tap at the bottom once every week or so to let out the gunk.

not sure which water plants take up both nitrates and ammonia equally. most seem to prefer ammonia even with enormous ammounts of nitrate. I guess its an energy conservation thing. why convert nitrate back to ammonium to use it for energy when it is available in the raw form.

I guess this all explains why deep water culture works so well with just solids removal.

UVI raft aquaponics, or NFT applications... necessitate the removal of solids... which considerably lowers the amount of ammonia requiring conversion...

But both models generally utilise plants that grow by the end product nitrate... rather than ammonia directly...

Sure there are aquatic aquaria plants that grow directly from ammonia.... but as TCL says... they can cause huge problems in a recirculating system... such as aquaponics or RAS aquaculture...

And as such... they're never utilised.... although duckweed, usually in a seperated tank/bin can be in aquaponics...

In flood & drain aquaponics.... there just isn't a need to remove solids.... if stocking densities and filtration ratios are followed....

And there are benefits related to mineralisation within the growbed bio-filtration system...

Aquaponics is more akin to RAS aquaculture than aquaria systems... in operation and principle... and in terms of fish stock....

And be wary of some "aquatic" plants... such as water lillies... which can be poisonous to fish.... and many other which are invasive and usually declared noxious weeds...

its OK rupert, get back off your box.

somtimes people like to talk about things that are a little different. I'm getting pretty *frack* annoyed with getting shot down for even mentioning something a little different, or trying to introduce some different science based facts into the equation. by the way, how many fish have you killed this year?

Orcy... I'm not trying to "shoot you down"...

Just pointing out, as did TCL.... that there are problems associated with using aquatic plants in both aquaponics and RAS... and that generally, there not used for those reasons... and aren't generally required...

As to my fish deaths... yep I've had more than I should have and would have liked...

One incidence in a transport tank... due to senility... where I forgot to turn on the air...

Another recent occasion in a holding tank where a storm ripped out the airline...

And my Barra system where I was over-stocked/under filtered... and had neglected to redress the situation when I should have....

None of the occasions involved a properly configured, and properly stocked aquaponics system...

And I posted accordingly....in the hope that others would learn the lesson of appropriate stocking densities, filtration and getting of your arse and doing things properly from the start...

Two of the occasions highlight the importance of sufficient aeration... and how quickly fish deaths can occur...

And the other the importance of planning, correct configuration and implementation...

All the aquatic plants in the world... wouldn't have altered the outcome of any of the events...

And your point is??