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

[jnms]

There maybe an obvious reason to this, but why don't liquid plant fertilizers get absorbed into the filter media?

 

[mike os]

Filters don't absorb, they convert biological waste products (ammonia ) into other products (nitrite & nitrate )

materials such as carbon zeolite etc adsorb many compounds including fertilisers, if you use carbon & fert save your time & just chuck it in the bin LOL

 

[jaycat]

I have a question then Mike os, if I have a carbon sponge in my internal filter, I dose with tpn+ should I take the carbon sponge out?

Thanks

 

[aaronnorth]

carbon ponges are pointless, i dont see how they work. Charcoal carbon is better, it is porous which absorbs the metals in it - sponges dont act like this.

Take carbon out. It is ok to have it under the substrate as the carbon will hold nutrients in and the plant roots will attach to this retrieving nutrients from it.

 

[Nick16]

so aaron you recomment putting a carbon sponge under the gravel? cut up?

 

[aaronnorth]

charcoal carbon (activated carbon)

 

[pastabake]

The whole point of carbon whether it be in a granular form or coated on a sponge has nothing to do with absorption

Chemistry The process by which one substance, such as a solid or liquid, takes up another substance, such as a liquid or gas, through minute pores or spaces between its molecules. A paper towel takes up water, and water takes up carbon dioxide, by absorption.

The sole use for activated carbon is because of this process adsorption

The process by which molecules of a substance, such as a gas or a liquid, collect on the surface of another substance, such as a solid. The molecules are attracted to the surface but do not enter the solid's minute spaces as in absorption. Some drinking water filters consist of carbon cartridges that adsorb contaminants.

So as far as activated carbon goes, whatever form its in, the principle is just the same ... overall efficiency comes down to active surface area and as such a carbon sponge has a pretty big accessible surface area - other forms may theoretically have a potentially greater area but this depends upon other factors such as clumping.

Not that any of this matters as routinely using activated carbon is pretty pointless unless you replace it regularly, and as it happens unless you live in an acidic area. As the bioavailability and toxicity of metals is somewhat dependant upon pH.

There is simply no point in putting carbon into your tank under the substrate as any nutrients that it takes up will have come from what you have added in the first place. Also if you have plants then DOC produced from leaf litter will in itself do a pretty good job of locking metals away.

 

[KraKen]

The purpose of carbon in the substrate is to adsorb nutrients from the water column so that algae cant's use them plants can still get to the nutrients because thier fine root hairs penetrate the carbon granules

 

[Dave Spencer]

There is simply no point in putting carbon into your tank under the substrate as any nutrients that it takes up will have come from what you have added in the first place......

There is a very good point in using carbon under the substrate. It makes nutrients available to plants through their roots, as well as via the water column. This allows more room for error in water column dosing, and having nutrients available via the water column and substrate brings the best results in terms of plant growth. If what you are saying is true, then substrates such as ADA Aqua Soil would also be pointless.

The purpose of carbon in the substrate is to adsorb nutrients from the water column so that algae cant's use them plants can still get to the nutrients because thier fine root hairs penetrate the carbon granules

This is incorrect. The purpose of carbon, or any nutrient rich substrate, is as I mentioned above. Very few planted tanks would work because they would become algae farms, yet this is not the case. Plenty of people, including myself run ferts in the water in excess of the plant requirements to make them non limiting to plant growth. If I want algae in my tanks, all I need to is run the water low in ferts. This takes a little time in tanks with nutrient rich substrates, though. In my sand tanks, it takes no time at all.

Dave

 

[aaronnorth]

There is simply no point in putting carbon into your tank under the substrate as any nutrients that it takes up will have come from what you have added in the first place. Also if you have plants then DOC produced from leaf litter will in itself do a pretty good job of locking metals away.

Like Dave says, it makes the nutrients accessible to the roots.

 

[pastabake]

There is a very good point in using carbon under the substrate. It makes nutrients available to plants through their roots, as well as via the water column. This allows more room for error in water column dosing, and having nutrients available via the water column and substrate brings the best results in terms of plant growth. If what you are saying is true, then substrates such as ADA Aqua Soil would also be pointless.

I know nothing about ADA Aqua Soil ... what I do know is that your statement regarding carbon just doesn't make sense.

 

[aaronnorth]

It does make sense.

when keeping plants, you either dose in the water column heavily (to make up for the loss of nutrients in the substrate- hence the statment less room for error), or just in the substrate, or both - which is better.

When we dose nutrients in the water column, the carbon in the substrate will take in some of those nutrients, the plants roots will then penetrate it and get nutrients from the carbon which in turn produces healthier plants.

ADA (aqua design amano - product designed by the famous aquascaper 'Takashi Amano') aquasoil is a specially designed substrate for plants whih contains nutrients. If carbon is pointless to put it there to make nutrients available for roots, then so would aquasoil - and all the other plant substrates on the market.

 

[Dave Spencer]

I know nothing about ADA Aqua Soil ... what I do know is that your statement regarding carbon just doesn't make sense.

Substrates such as Aqua Soil and Eco Complete have a high cation exchange capacity (CEC). I know of one or two people that use carbon under sand, in the substrate to attract positively charged ions such as Mg and K and make them available to plant roots, alongside constant replenishment via water column dosing. This way, the plants are getting their nutrients from two sources, which generally gives the best growth rates.

All the reading I have done on the action of activated carbon adsorbing plant nutrients show its effects to be minimal, and I doubt its abilities as a replacement for a clay based soil such as Aqua Soil.

Dave.

 

[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?

 

[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?

No, but the active carbon would* absorb some of the toxic/harmful compounds produced by bacteria in severely anaerobic soil. This could help while the soil matures. In a matured, planted substrate, any hydrogen sulphide and methane produced at the bottom should be oxidised well before it gets released into the water column.

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.

As far as cation exchange capacity is concerned, I'm under the impression that peat in the substrate does exactly what active carbon does.

* edit: let's add the word "hopefully" in there. Different types of carbon adsorb different molecules, and cation exchange sites will generally release their captive molecules if they encounter a molecule that fits in even better. This in turn depends on other factors like pH.