# What is 'clay'?



## smatos69 (May 18, 2018)

Hi all.
This is my first thread/post on this forum - hope I don't break the rules...

I'd like to know if clay is always clay, or if only some are good for aquaria. For instance, can I use broken and grinded flower pots in a substrate? Will it be beneficial?

Thanks in advance.


----------



## hoppycalif (Apr 7, 2005)

Welcome to APC! You haven't broken any rules, yet, which probably puts you in a unique position!

You got me curious enough to use Google. https://en.wikipedia.org/wiki/Clay To me clay is something I know when I see it, but I can't define it. I do know that fired clay, like terra cotta, is not equivalent to clay in a soil. So, if you break up flower pots you don't get clay, but some commercial substrates are largely fired clay. That tells me that you could make a usable substrate by using a hammer to bust a lot of old flower pots.


----------



## smatos69 (May 18, 2018)

Hi, all.
@Hoppy, thanks for your input.

Technically clay is any particle below 63micron size, but in aquaristics clay is 'a sort of' gravel, with high adsorption capacity. I was wondering if it would be so simple - flowerpots. My thought was that after burning/baking, the clay woud change chemical properties and be useless in retaining nutrients.

I'm preparing a 1200 litter (330G) aqua... When I start aquascaping I'll mix some broken clay pots into the substrate and cap it with gravel.
👍


----------



## DutchMuch (Apr 12, 2017)

Arent aquaponic substrates fired clay? the ball things? lol


----------



## Michael (Jul 20, 2010)

Terra cotta is high fired clay. A lot of low fired clays are used in horticulture and aquaria: Safe-T-Sorb, Turface, cat litter, laterite, etc. All of these retain the high cation exchange capacity (CEC) that make clay useful to us. I don't know if terra cotta is the same, but it certainly can't hurt.


----------



## smatos69 (May 18, 2018)

DutchMuch said:


> Arent aquaponic substrates fired clay? the ball things? lol


The brownish balls the size of a fingernail? I never thought of it...

If so, it should be good for underwater nutrient trapping - as long as no fertilizers come with it. And using plain clay from flower pots should keep it clean from additives.

Well, thanks guys! I know what I'll use as a substrate next tank - or at least mixed in the ditto.


----------



## EDGE (Feb 28, 2004)

smatos69 said:


> The brownish balls the size of a fingernail? I never thought of it...
> 
> If so, it should be good for underwater nutrient trapping - as long as no fertilizers come with it. And using plain clay from flower pots should keep it clean from additives.
> 
> Well, thanks guys! I know what I'll use as a substrate next tank - or at least mixed in the ditto.


Aquaponic / hydroponic clay balls doesn't "absorb" nutrients in the same way as the other clay that has a high cation exchange capacity (CEC). They are inert, very light and can float until they get water logged.

https://en.wikipedia.org/wiki/Cation-exchange_capacity


----------



## DesH (Jun 14, 2016)

I don't think that all Clays are the same . There seems to be some difference depending on where they are from . The most useful from our point of view is Laterite which is a tropical clay . Fired clays like Terracotta and Expanded Clay Pebbles are inert and will have neither a positive or negative effect .


----------



## Sherryazure (Jun 20, 2003)

smatos69 said:


> Hi all.
> This is my first thread/post on this forum - hope I don't break the rules...
> 
> I'd like to know if clay is always clay, or if only some are good for aquaria. For instance, can I use broken and grinded flower pots in a substrate? Will it be beneficial?
> ...


I just happen to have a massive background in ceramics and was instructed (while in NYC) with one of the best professor ever (Susan Peterson) master's level of expertise in ceramics chemistry.

Clay is basically one of many forms of soil. These come about as the river systems starting at mountain tops collect minerals and grind them down and they are deposited (over much time). It's actually very complicated.

Porcelain for example - usually white (but can come in many colors with added minerals) or when thin (as in a pot) it is almost glass-like and transparent. Its name has nothing to do with the the type of clay but the fact that with less minerals it can be fired at much higher temperatures in the Porcelain range.

https://www.hunker.com/12003887/different-types-of-clay-soil

Once the clay (soil body with added minerals depending on what one wants for the end result) is "fired" (and each "clay body" has a different firing range) then the composition of the molecules in the original wet clay (which changes as it dries) is set!

So NO pottery - terra cotta so named for it's much lower firing range, (and red due to minerals added and if fired higher would "melt" into a puddle) can not "reconstitute" back to it's original form (unbreak those molecules that are now "fixed" due to being heated at high temperature).

You can use it as a substrate if you want oxygen underneath but gravel will work better or as a filler. Like those who use broken plates (made from clay) or pottery as fillers at the bottom of land plants to create a drain for the container with finer and finer gravel added upwards.

Unless you have a really large aquarium, this would MHO be overkill.


----------



## Sherryazure (Jun 20, 2003)

smatos69 said:


> Hi all.
> This is my first thread/post on this forum - hope I don't break the rules...
> 
> I'd like to know if clay is always clay, or if only some are good for aquaria. For instance, can I use broken and grinded flower pots in a substrate? Will it be beneficial?
> ...


..................................

First forgive please editing and typos, I find it very hard to write in small spaces.

I just happen to have a background in ceramics and was instructed long ago (while in NYC) with one of the best professor's ever (Susan Peterson) master's level of expertise in ceramics chemistry. I was a "lab assistant" and made the various clay bodies and glazes. (But forgive in advance as my books are long stored)

But first, just as in one's land garden, clay soils can be a HUGE problem so to would it be in the aquarium, unless one uses additives. (due to the nature of the molecules there is little room for oxygen or anything else). Yet there some plants, land and aquatic that do well in such soils with added bodies.

...........................................

This site is excellent as a resource (often burried in searches) and this includes the substrate bodies for aquariums (differing depending on the plants).

http://www.wetwebmedia.com/PlantedTksSubWebIndex/soilags.htm

On the Use of Soil In Aquarium Gardening

....................................

Unless you want to be advanced in your knowledge in your aquarium substrate and "mix" your own which may include clay bodies, my suggestion would be to find the proper Pre Made soils for the plants you desire and go from there.

Pond keepers often use clay bodies (and other types of "soil") for plants in the pond. It is always a mix of this or that by degrees based on the need of each plant type.

.................................

Top 12 Plants That Grow Well In Clay Soil
Posted by Farhan Ahsan on August 30, 2014 in Flowers |

http://theselfsufficientliving.com/top-12-plants-grow-clay-soil/

...............................

Clay is basically one of many forms of soil. These come about as the river systems starting at mountain tops collect minerals and grind them down and they are deposited (over much time) along the river route. The further away from the source the more minerals are added and the composition. It's actually very complicated.

Porcelain for example - usually white due to Kaolin "clay" or certain minerals is white as it is derived near the top of these river deposits without the added minerals that would alter the colors with the minerals (eroded rocks in river beds) further down. This is why when the project is thin (as in a pot) it is almost glass-like and transparent. Its name has nothing to do with the type of clay but the fact that with less minerals it can be fired at much higher temperatures in the Porcelain range. Industrial clay bodies are another matter (very high temps).

.............................

Porcelain is a ceramic material made by heating materials, generally including kaolin, in a kiln to temperatures between 1,200 and 1,400 ̊C (2,200 and 2,600 ̊F). The toughness, strength, and translucence of porcelain, relative to other types of pottery, arises mainly from vitrification and the formation of the mineral mullite within the body at these high temperatures.

These natural clay bodies were abundant in China and it was unique. The Chinese did not allow this "secret" out (ie selling the clay body) and many "faux" bodies were created to try to replicate it's unique and rare characteristic - but they never came close. Visit any major museum with these amazing Ceramics and one can see their uniqueness.

..........................................

https://www.hunker.com/12003887/different-types-of-clay-soil

Once the clay (soil body with added minerals depending on what one wants for the end result) is "fired" (and each "clay body" has a different firing range) then the composition of the molecules in the original wet clay (which changes as it dries) is set!

So NO pottery - terra cotta so named for it's much lower firing range, (and red due to minerals added and if fired higher would "melt" into a puddle) can not "reconstitute" back to it's original form (unbreak those molecules that are now "fixed" due to being heated at high temperature).

You can use it as a substrate if you want oxygen underneath but gravel will work better or as a filler. Like those who use broken plates (made from clay) or pottery as fillers at the bottom of land plants to create a drain for the container with finer and finer gravel added upwards.

Unless you have a really large aquarium, this would MHO be overkill.


----------



## ChuckM (Mar 19, 2020)

Great post Sherry. I also have a strong background in clay and ceramics, but as an artist who's excavated and processed their own for forming and firing art of dubious distinction.
But I also have been keeping two community tanks with a baked clay product as a substrate and I'm mostly satisfied with how it's worked out.
I was inspired to try this by the likes of Jalabert, Novak and Jay of Jay's Aquarium. Especially Jay who very cleanly described why it's valuable. But in all cases the point of using baked clay was to promote the growth of anaerobic bacteria for denitrification.


From an aquarist's standpoint I just want to point out the distinction between clay and baked (fired) clay. Raw clay probably has no place in an aquarium because it basically remains as a dense mush and that's what'll happen (as many have found out) if you use a kitty litter product that's not explicitly baked. When clay is fired it becomes a porous stone which provides a good habitat for anaerobic bacteria. I suspect the "biological media" we all get with our filters that we carefully age is an attempt to accomplish the same thing. I've chosen to make that concept into a deep bed (3") substrate with a 3:1 ratio of Oil-Dri and Eco-Complete (with a 1" plenum). My nitrate levels run between 20 and 40 ppm depending on the test I use, and apparently the phase of the moon.


----------



## hoppycalif (Apr 7, 2005)

Welcome to APC! We have been discussing the use of non-aquarium substrate materials in place of the very expensive substrate materials as long as i have been playing with planted aquariums. People seem to switch back and forth on whether they like using things like cat litter or not. My experience with Safe T Sorb (baked clay) has been very good for the past 5 months, but that's not a long time.


----------

