# Too much clay in diy sub



## rebel (23 Jun 2016)

Hi everyone, I use a diy substrate with sand, blood and bone fertiliser, calcium co3 chips and clay, the fert tabs I use have a lot of clay. I use fert tabs almost every 3 months for all the crypts and rooted plants.

My query is whether I can add too much clay to the soil. I know that in terrestrial soil too much clay is bad but is it the same for aquatic soil .?

Appreciate your thoughts.


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## Tim Harrison (23 Jun 2016)

I've found that aquatic composts seem to have a large clay content and after mineralisation there is very little organic matter left.

However, I personally don't like too much clay in the mix. I prefer a light friable mix, one that has a crumbly texture ideal for root development.
Sediments are anaerobic by nature but a friable mix allows for some circulation, nutrient transference and gas exchange and therefore microbial activity. So if anything I tend to add a large amount of humic or organic content (peat mainly). That is along with grit or sand.

But one of the joys of soil tanks is experimentation, so go with what you think might work best for your tank. There are many routes to success


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## zozo (23 Jun 2016)

To much clay as well to much sand can become a problem when cloged, if it forms a very dense almost impenetrable anearobic layer.. As Troi says, as long it's a complete crumbly texture there aint much to worry about.. Take for example Akadama soil, also used very succesfully in aquarums is solely clay particles, but it's a very hard small particle. I'm already using it for over a year also with clay fert tabs, no worries i love it when it comes to plant growth. Aesthetically ?? Depends, not always..


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## rebel (23 Jun 2016)

Thanks guys.

Unfortunately we don't have Akadama in Australia. It sounds awesome.

The question relates to an already established sub where I keep adding clay based fert tabs.

After what I have heard from you , I will switch to non-clay based tabs. I still have some ADA tabs somewhere (have lost the damn things!) and some pellets of organic ferts which I will use for now. I also have osmocote but don't like the left over blue pellets from them!


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## dw1305 (23 Jun 2016)

Hi all, 





zozo said:


> if it forms a very dense almost impenetrable anaerobic layer..





Troi said:


> Sediments are anaerobic by nature but a friable mix allows for some circulation, nutrient transference and gas exchange and therefore microbial activity.


That would be my concern as well. It would depend a little bit on the plants how much of an issue it was.

Emergents (like _Cyperus _or_ Rhizophora_), or plants with floating leaves (like_ Nymphaea_) that grew in deep water, often have a system of <"aerenchyma">, which as well as adding buoyancy, supplies oxygen to roots that are growing through anaerobic substrates.

Although most of the oxygen that is being conducted to the root is from photosynthesis wholly submerged plants don't have the luxury of access to atmospheric gas levels, so that in sediments with negative REDOX potentials oxygen availability can be a problem. 

cheers Darrel


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## rebel (23 Jun 2016)

Do you guys use clay based tabs in DIY substrates? The problem with  my sub is that I made a mistake about the grain size of the capping layer. It's far too fine and I suspect my water column ferts (plentiful) are not really reaching the roots.

I have plants such as Erio shiga which really appreciate root tabs in this sub. Same plant in Black Earth Premium (commercial), I can just fert the water column and things are ok.


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## rebel (23 Jun 2016)

dw1305 said:


> Hi all, That would be my concern as well. It would depend a little bit on the plants how much of an issue it was.
> 
> Emergents (like _Cyperus _or_ Rhizophora_), or plants with floating leaves (like_ Nymphaea_) that grew in deep water, often have a system of <"aerenchyma">, which as well as adding buoyancy, supplies oxygen to roots that are growing through anaerobic substrates.
> 
> ...


Appreciate your thoughts. I learnt a new word; Aerenchyma! and realized that I have eaten these aerenchyma when I ate lotus shoots.


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## zozo (23 Jun 2016)

rebel said:


> Do you guys use clay based tabs in DIY substrates? The problem with my sub is that I made a mistake about the grain size of the capping layer. It's far too fine and I suspect my water column ferts (plentiful) are not really reaching the roots.



This is an intresting point a like to ponder about why other people would ponder about it so much when it regards aquarium soil.

Take for example terrestrial plants, they should stay on a well draining soil you can give them water from the top or from bellow. Depending on the plant one prefers this the other that.. Anyway a aquarium substrate should be equaly as well draining if even not more.. I actualy see no reason why ferts wont penetrate the soil when there is a body of water containing this fert above it. After all it's the same water making it wet and if the soil has good circulation properties it should be fine.

Roottabs serve the purpose of giving plants which rather have more than the lean ferts over the water collum we give and so we use root feeding to prevent the water collumn to become to rich in ferts. In comparison with regular ferts used for terrestrial fertilization it's about 2 times as much in contents of what we use. That would be way to much and to risky to put so much in the water column.

For example a regular fert off the shelf for plants planted on regular dirt soil contains the following
2% N (total)
0,5% NH4
2%  NO3
2% P2O5 - (0.8% P)
3% K - (4% KO)
0.5% Mg - (0,8% MgO)
0,5% S - (1% SO3)
0.006% B
0.001 Cu
0,01% Fe (DTPA)
0.004 Fe(EDDTA)
0.01% Mn
0.001 Mo
0.005% Zn
That's about twice as much NPK as the complete tropica fert for aquariums.

Most roottabs are clay based, just because the clay has a high CEC and holding the ferts in to release them slowly to the plants needs instead of leaching them out to the water column.. That's the whole point in using clay in the substrate in the first place, because of it's high CEC value and capacity to take up and store ferts.

But that's just my thought about it and that's why i sufice with inert substrates to put in my tanks. I always can put in if its necessary, needing to take out, now that's where the problem starts..


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## dw1305 (24 Jun 2016)

Hi all,





zozo said:


> Anyway a aquarium substrate should be equaly as well draining if even not more.. I actualy see no reason why ferts wont penetrate the soil when there is a body of water containing this fert above it. After all it's the same water making it wet and if the soil has good circulation properties it should be fine.


 I think that is right. 

If you have a very clay rich substrate you won't get any lateral movement through the substrate, which may lead to local depletion of nutrients. Anaerobic areas in the substrate are fine, they may help to reduce oxides and make nutrients available, but a very fine grained substrate (like a clay) might lead to large anoxic areas, and this opens up the potential for H2S production from any organic material etc.

cheers Darrel


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## zozo (25 Jun 2016)

Back in the days i only used washed river sand topped with gravel.. That was also about it when it comes to availabiliity, planted tanks and strange scapes as we know them today weren't yet so popular. Books didn't realy mention scaping styles or banking up substrate to high levels. At least not the regular books in the library or shops. So these where relatively flat scapes with the substrate not exceding 4 inches in height at the back.. Sand is also a substrate prone to clogging and produce anoxic areas, taking it's height in account this can take a rather very long time before this happens and if it is well planted and rooted it might never be the case. At least personaly i never experienced it with using sand and those tanks stoot for many years. If i took down a tank it was because i got bored with the setup and not because of substrate troubles.
It all were low tech and never used a roottab nor any additional ferts.. And also had a massive carpet of dwarf sag after a year and a lush background of vallis, parrot feathers and swords etc.. These were my experiences as a beginner back in the 70's. Digital photography wasn't realy available in my beginner times even a good photocamera was out of reach for the avarage working class, i would need to dig very deep into family archives to find pics with one of the tanks on them. if i ever do, i would love to make a scan and show them.

Anyway this also goes for substrate containing sand and clay, if it's not banked up to high, well planted and well rooted, then you do not need to worry so much..


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