Substrate Life Span

[Atlas]

Hello everyone,

I have been looking though the tutorials and journals and the wealth of information on here is great.

I do have a question that I cant seem to find answer too though. After reading the EI dosing using dry salts and the setting up a high tech planted tank I feel I know what I need to do to setup a planted tank and maintain with nutrients.

My question is how long does a nutrient rich substrate keep feeding the plants?
Does the dosing of the water column also ‘charge‘ the substrate?

Being a bit green the thought of having to replace spent substrate and the logistics of that is a little daunting at this stage.

Thanks

 

[Tim Harrison]

It depends on the substrate, amongst other factors, some have a higher nutrient conc than others. ADA AS Amazonia nutrient content is pretty high, but it tends to become depleted of Nitrogen fairly quickly and then Liebig's law of the minimum kicks in, for instance.
However, if you're water column dosing it shouldn't ever become a problem. And yes water column dosing can recharge a substrate, but again it depends on the substrate. If it has a high CEC it will recharge quite readily. For instance, Flourite has a CEC of around 1.7 me./100g compared to say ADA AS which has a CEC ranging from 24.5 - 27.5 me./100g, so AS will recharge fairly readily, whereas Flourite not so.

I've often rinsed, dried, and reused ADA AS with great results. In fact I prefer it used since there isn't so much of an ammonia spike. Basically, if you water column dose fertz, EI or whatever, you never really need worry about your substrate becoming depleted of nutrients. And even if it does most plant will folia feed quite happily; you can grow plants in marbles providing you water column dose.

 

[Atlas]

Thank you Tim that has set my mind at rest.

 

[Simon Cole]

People often say that plants can absorb 400 times more nutrients from their roots, but I don't think this means the roots do not extract nutrients primarily from water in the substrate.
Tim - do you think that substrates can accumulate too many nutrients, or possibly become toxic to the root environment? I mean due to absorption as opposed to cation exchange.

 

[Zeus.]

do you think that substrates can accumulate too many nutrients

No as this wouldnt be an issue IMO

possibly become toxic to the root environment?

Yes - if the water change (WC) is insufficient. The AS picks up the toxins as well as the nutrients which helps buffer the Water column. If the WC isnt enough the levels of toxins stored in the AS could become toxic to the plants.

Hence the weekly 50% WC adivised by T Barr in EI fert dosing which resets the fert levels and the toxin levels to safe/optimal limits/levels

 

[Tim Harrison]

Good question; if we're talking about substates specifically designed for planted aquaria I doubt it. However, I suspect ADA AS, when new, can cause nutrient/ammonia burn in some species. For instance, I think that perhaps it's too rich for Stauro; I'm not the only one to observe that either. However, a couple or three weeks later it becomes depleted enough for Stauro to grow quite happily. I guess that is why some folk recommend a 2-3 week plantless start when using AS.

 

[Tim Harrison]

I think the 50% water change is to remove organic metabolic wastes from the water column as well as reset nutrient levels. For toxic levels of nutrients to build up in the substate the CEC would have to be very high.

 

[dw1305]

Hi all,

For toxic levels of nutrients to build up in the substate the CEC would have to be very high.

I think toxicity is likely to be largely an oxygen issue, and could potentially occur in a lot of different substrates.

If you have a mineral rich substrate, that becomes anoxic under reducing conditions, then you can get toxic levels of many micro-nutrients. There is lots of work on this in water-logged terrestrial plants, often looking at <"iron (Fe) toxicity"> particularly in crop plants and most specifically Rice (Oryza sativa).

It is one of the reasons that emergent aquatic plants have evolved aerenchyma and leaky roots. The oxygen leaks into the rhizosphere and oxidises (the potentially toxic) ferrous (Fe++) iron ions into insoluble ferric (Fe III) oxides.

cheers Darrel