So Why Don't Liquid Ferts Get Absorbed Into The Filter?

[pastabake]

I would guess that ADA's soil is not clay based as it claims to be black earth based

The dark earth, called terra preta, was produced by Amazonian people who slowly burned their waste by smoldering it, thousands of years ago.

Also ADA say that their soil will have an effect on the pH and KH of the water. So you might as well use peat under the substrate, in fact I'd suggest that it would be better than carbon on its own.

The carbon sink and buffer idea would work if it wasn't for the constant overdosing of the water column. The carbon will be getting its nutrients from the water column (I note that the ADA product is already nutrient loaded) and will act like a buffer to begin with by taking out excess nutrients from the water, or from the substrate around it. After a while though it will become nutrient saturated and only be of use as a sink. However, as the water column is being constantly overdosed there will never become a time when its nutrients will actually be needed.

So while I could agree that using carbon in the substrate might be a good idea if you were erratic with your nutrient dosing and you didn't go in for overdosing on a regular basis in most other situations it would basically be pointless and probably not as good as using peat or possibly even a real soil.

edit - also over time any substrate based upon Cation exchange has the potential to become saturated with heavy metals and other non useful or over abundant substances, rather than the nutrients essential for plant growth. This may especially be a problem for the high tech overdoser that demands crystal clear water and a clean detritus free surface to their substrate.

 

[Dave Spencer]

I would guess that ADA's soil is not clay based as it claims to be black earth based. Also ADA say that their soil will have an effect on the pH and KH of the water. So you might as well use peat under the substrate, in fact I'd suggest that it would be better than carbon on its own.

I only know of one test carried out on Aqua Soil, and it is clay based according to the test. It certainly feels like clay.

The carbon sink and buffer idea would work if it wasn't for the constant overdosing of the water column. The carbon will be getting its nutrients from the water column (I note that the ADA product is already nutrient loaded) and will act like a buffer to begin with by taking out excess nutrients from the water, or from the substrate around it. After a while though it will become nutrient saturated and only be of use as a sink. However, as the water column is being constantly overdosed there will never become a time when its nutrients will actually be needed.

If nutrients are available at the roots as well via leaves, then plants will use both sources available to them, not just the water column. Plants in an inert substrate will tend to put more effort in to leaf production rather than roots to better source the available nutrients, and vice versa.

edit - also over time any substrate based upon Cation exchange has the potential to become saturated with heavy metals and other non useful or over abundant substances, rather than the nutrients essential for plant growth. This may especially be a problem for the high tech overdoser that demands crystal clear water and a clean detritus free surface to their substrate.

Several high CEC substrates have been used in high tech tanks for a long time now. I have never heard of this happening. My guess is that plants will take in just about anything out there.

Carbon has more than one use in the planted tank, whether it be in the filter of an immature tank helping to fight off initial algae, or as a supply of nutrients to plant roots. Cat litter works well, also......

Dave.

Edit: What part of Luton are you from? I`m from Lewsey Farm.

 

[Dave Spencer]

Plant roots of many/most/all root-feeding species will grow into anaerobic soil and maintain its redox potential above severely anoxic conditions by pumping oxygen into their roots. In fact, they require a degree of anoxia around their roots for optimal nutrient intake, e.g. iron becomes available to plants under anaerobic conditions. Swords of various sizes are awesome at this as they grow deep roots over a wide area around the plant.

I`m a little confused by this. Considering how much O2 is produced in the substrate by plant roots, where do the anoxic conditions come from?

Dave.

 

[Mr Bliss]

Plant roots of many/most/all root-feeding species will grow into anaerobic soil and maintain its redox potential above severely anoxic conditions by pumping oxygen into their roots. In fact, they require a degree of anoxia around their roots for optimal nutrient intake, e.g. iron becomes available to plants under anaerobic conditions. Swords of various sizes are awesome at this as they grow deep roots over a wide area around the plant.

I`m a little confused by this. Considering how much O2 is produced in the substrate by plant roots, where do the anoxic conditions come from?

Dave.

I may be wrong, since it's been years since I took classes on the subject, but I'm under the impression that the oxidized rhizosphere only reaches a few millimeters from the root surface during photosynthesis and shrinks to a paper thin layer at night time. The oxygen is depleted rapidly by microbes (and reduced compounds such as sulfides, if they are present) in the soil. So unless you have a tank planted very densely with root-feeding plants, wouldn't there be quite a few anoxic pockets here and there, with an almost completely anoxic substrate in the morning before the lights go on?

 

[andywg]

Would placing carbon beneath the sand, cause it to draw down carbon dioxide and other gasses, thus reducing the potential for anaerobic decay pockets?

I have never understood the desire to avoid anoxic conditions in the substrate in FW tanks. In SW tanks we often strive for anoxic conditions as anaerobic bacteria convert nitrate to nitrite to ammonia to nitrogen gas, thus "completing" the nitrogen cycle and slowing the build up of nitrates.

There is occasionally mention of hydrogen sulphide but this denatures in water once exposed to oxygen (which it will be before leaving the substrate).


With regards to the carbon substrate, I have seen it suggested by people such as nmonks and bignose that carbon can reach its maximum state of adsorbtion within 24 to 48 hours, so I am unsure how it would actually assist with a constant dosing regime when it would fill so quickly.

 

[jnms]

Would placing carbon beneath the sand, cause it to draw down carbon dioxide and other gasses, thus reducing the potential for anaerobic decay pockets?

I have never understood the desire to avoid anoxic conditions in the substrate in FW tanks. In SW tanks we often strive for anoxic conditions as anaerobic bacteria convert nitrate to nitrite to ammonia to nitrogen gas, thus "completing" the nitrogen cycle and slowing the build up of nitrates.

I would be interested in knowing why this is too...

Surely it can't merely be down to the salt? There must be other conditions that factor in. Or is it just one of those 'myths' and anoxic conditions don't actually harm FW fish?

 

[Mr Bliss]

Would placing carbon beneath the sand, cause it to draw down carbon dioxide and other gasses, thus reducing the potential for anaerobic decay pockets?

I have never understood the desire to avoid anoxic conditions in the substrate in FW tanks. In SW tanks we often strive for anoxic conditions as anaerobic bacteria convert nitrate to nitrite to ammonia to nitrogen gas, thus "completing" the nitrogen cycle and slowing the build up of nitrates.

I would be interested in knowing why this is too...

Surely it can't merely be down to the salt? There must be other conditions that factor in. Or is it just one of those 'myths' and anoxic conditions don't actually harm FW fish?

I think the main reasons some aquarists fear anoxic pockets are: 1) the potential for H2S contamination and 2) incomplete denitrification where nitrates are converted back to nitrite/ammonia without making it all the way to nitrogen gas.

1: Hydrogen sulfide would probably be less of a threat in marine aquariums, given that they typically have very strong water circulation along with powerful aereation inside protein skimmers. H2S is highly reactive and doesn't like being dissolved in water; in a typical marine aquarium it would be rapidly oxidized into sulphates or escape the water column.

2: Bacterial denitrification does not happen efficiently in freshwater. The efficiency of denitrification improves with increased salinity, and in fact reaches its peak in salt concentrations much higher than normal marine salinity. I'm not familiar with the underlying chemistry, but I do know that the main denitrifying bacteria in saltwater are different species than the bacteria in freshwater substrates. In a marine tank you can use a deep sand bed to reduce nitrates to nitrogen gas. In a freshwater tank a similar substrate would just produce nitrites and ammonia, partially undoing the work of your filter. So we really only have two ways to get rid of excess nitrogen in our tanks: water changes and plants. Which is the case in nature as well (nitrogen is either taken up by plants or "water changed" into the sea).

edit: heh we've strayed pretty far from the original topic.

 

[pastabake]

Dave - I'm living in Leagrave at the moment, moved here from N.Wales (Gerlan) wish I hadn't.

You might be right about the ADA soil but from their website it's clear that they want you to believe it's made from Black earth. I spoke to a soil scientist about this and she assures me that due to its carbon structure black earth is extremely good - for agriculture at least. However she also pointed out that any idea of it being either a buffer or nutrient sink in an aquarium situation was fanciful at best, because the rate of nutrient exchange from the water to substrate would be extremely slow ... unless you had some way of moving water through it, which might result in less than clear water.

 

[aaronnorth]

The thing is with aquasoil, it is highly porous, so water moves through it more easily than with a normal substrate like gravel which helps with the nutrient exchange,

when s/he said 'extremely slow' - how slow is this? Plants dont need a massive amount of nutrients to their roots, and they will use whatever is taken in the substrate, and over time the nutrients would build up in the soil anyway, you also have to remember that AS comes 'supplied' with nutrients in it, which again helps with the situation.

EDIT: would the same be said for carbon under the substrate? If so, then this would also be pointless in the filter correct? senn as it is so slow to exchange from the water to the carbon.

 

[pastabake]

Porosity wouldn't make a difference ... there would still have to be a driver to make the water move through it, perhaps this is why some people use substrate heating.

 

[Dave Spencer]

Porosity wouldn't make a difference ... there would still have to be a driver to make the water move through it, perhaps this is why some people use substrate heating.

Substrate heating is an even deader duck than Luton.

I grew up on Lewsey Farm, but eventually moved to Rhosesmor in N. Wales.

Dave.

 

[RadaR]

Heating cables do squat. Waste of money and time. Make no difference at all.

 

[pastabake]

As it happens I use a vivarium heating mat (I can see no difference in principle between it and substrate heating cable btw) to heat my small 45l tank it works a treat and is hidden from sight. So obviously substrate heating isn't a waste of money, especially as I got it for free ... as to whether it has any use other than heating ... now that is the question.

In principle it would drive water through the substrate - unless you disagree with the laws of physics - thus making the carbon substrate work as a buffer and a sink so it would be a great idea if it wasn't for the fact that having a carbon based substrate is in itself pointless and a complete waste of money. I take it we all agree??

I wouldn't have wanted to grow up on Lewsey Farm either so you have my sympathies ... The last time I was in Rhosesmor it didn't exactly strike me as being the life and soul of the party.

 

[aaronnorth]

As it happens I use a vivarium heating mat (I can see no difference in principle between it and substrate heating cable btw) to heat my small 45l tank it works a treat and is hidden from sight. So obviously substrate heating isn't a waste of money, especially as I got it for free ... as to whether it has any use other than heating ... now that is the question.

I think they were referring to the heating cables doing nothing for plants, not for heating purposes.

 

[RadaR]

As it happens I use a vivarium heating mat (I can see no difference in principle between it and substrate heating cable btw) to heat my small 45l tank it works a treat and is hidden from sight. So obviously substrate heating isn't a waste of money, especially as I got it for free ... as to whether it has any use other than heating ... now that is the question.

In principle it would drive water through the substrate - unless you disagree with the laws of physics - thus making the carbon substrate work as a buffer and a sink so it would be a great idea if it wasn't for the fact that having a carbon based substrate is in itself pointless and a complete waste of money. I take it we all agree??

I wouldn't have wanted to grow up on Lewsey Farm either so you have my sympathies ... The last time I was in Rhosesmor it didn't exactly strike me as being the life and soul of the party.

Me thinks you should have a word with Tom Barr who has been doing studies on it...