Role of crushed coral in plant growth?

[JoeQ]

Is there a role crushed coral plays in plant growth other than buffering the KH of water? Does it provide other nutrients or aid in other processes of growth? 

[Mmiller2001]

It also adds calcium which is a component of GH. I see it as a source of instability.

[Seattle_Aquarist]

Hi @JoeQ

I have to agree with @Mmiller2001, crushed coral really should not be used in a planted tank.  It does add calcium which may or may not be needed depending upon local water supply but it also adds carbonate which increases the pH of the tank making the most common form of iron (EDTA chelated iron) such as used in Easy Green difficult if not impossible for the plants to uptake.  If a tank does need to increase calcium I encourage using Seachem Equilibrium (which contains calcium sulfate and magnesium sulfate) or just plain calcium sulfate.  If the dGH of a tank is low, and it is not caused by using RO water or water softener water then Equilibrium is probably the best because most tanks with low dGH have both low calcium and low magnesium levels.  -Roy

Edited August 15, 2022 by Seattle_Aquarist

[anitstuk]

Just like mentioned earlier, crushed coral adds calcium which can help shrimp and crayfish molt out of their shells. I personally don't know if it helps which plant grow though

Edited August 15, 2022 by anitstuk

[Anjum]

On 8/15/2022 at 4:03 PM, Seattle_Aquarist said:

but it also adds carbonate which increases the pH of the tank making the most common form of iron (EDTA chelated iron) such as used in Easy Green difficult if not impossible for the plants to uptake. 

Well shoot, I did not know that. At what pH is the EDTA uptake inhibited? 

[Seattle_Aquarist]

On 8/15/2022 at 9:36 PM, Anjum said:

Well shoot, I did not know that. At what pH is the EDTA uptake inhibited? 

Hi @Anjum

EDTA chelated Iron starts to drop off in availability at pH 6.2. At pH 6.7 about 1/2 of the iron in a fertilizer solution is available to plants.  At pH 7.0 about 15% of the iron is available.  By the time we get to pH 7.2 less that 10% of the iron is available.  And at pH 7.5 only about 3% of the iron in solution is available to the plants.  Coral is basically calcium carbonate which adds carbonate ions to the tank as it dissolves.  Carbonate ions in turn increase the pH.  This explains why so many issues of iron deficiency show up in tanks with crushed coral in the substrate.

Is crushed coral bad? No, it is fine in a livebearer tank since most (but not all) livebearers like hard, more alkaline water.  And there are some plant species that can tolerate alkaline conditions.  There are also types of iron that is not as adversely effected by elevated pH levels.  -Roy

[nabokovfan87]

Is there a database of PH that plants like? Maybe this is something useful for ACO to have in their website or something we can compile for ACO plants as an "advanced planted tank" tool?  The biggest one that stands out to me is how many people struggle with Scarlet Temple.

[JoeQ]

On 8/15/2022 at 7:03 PM, Seattle_Aquarist said:

Hi @JoeQ

I have to agree with @Mmiller2001, crushed coral really should not be used in a planted tank.  It does add calcium which may or may not be needed depending upon local water supply but it also adds carbonate which increases the pH of the tank making the most common form of iron (EDTA chelated iron) such as used in Easy Green difficult if not impossible for the plants to uptake.  If a tank does need to increase calcium I encourage using Seachem Equilibrium (which contains calcium sulfate and magnesium sulfate) or just plain calcium sulfate.  If the dGH of a tank is low, and it is not caused by using RO water or water softener water then Equilibrium is probably the best because most tanks with low dGH have both low calcium and low magnesium levels.  -Roy

Interesting,  that might tie back to my water silk problem last year. My question now is it Iron from the water column only,  or does CC affect absorbing Iron through roots in the substrate?

[Seattle_Aquarist]

Hi @JoeQ

Down the rabbit hole!

Iron used by plants comes in two forms, ferrous (Fe2+) or ferric (Fe3+).  Plants can absorb iron (ferrous or ferric) either through the roots (both types) or through the leaves (ferrous only).  Most herbaceous plants utilize iron in the ferrous (Fe2+) state for various internal processes.

Plants utilize iron in the ferrous (Fe2+) state however the Fe2+ ion is not very stable and will rapidly oxidize into a ferric (Fe3+) ion state.  Iron in the the ferric state can be utilized by plants as well but first must be converted to the ferrous state.  This is done in the root zone where various biological processes can convert ferric ions into usable ferrous ions.

EDTA chelated iron is a molecule of the ferric (Fe3+) iron bonded to a chelate molecule.  This allows the ferric iron to be utilized by plants in the root zone where the chelate molecule is 'stripped' from the ferric molecule.  Then the biological process can convert the ferric ion into usable ferrous ions. 

Unfortunately the bond between the EDTA chelate molecule and the ferric (Fe3+) iron is not very strong.  The chart below shows the effect of increasing pH and the 'breaking' of the chelate - ferric iron bond.  When the bond is broken the ferric molecule is free to bond with any other available molecule, typically oxygen.  This forms a precipitate of ferric hydroxide (insoluble particles) that can indeed be visible.  Hope this helps! -Roy
 

Edited August 16, 2022 by Seattle_Aquarist

[JoeQ]

On 8/16/2022 at 12:26 PM, Seattle_Aquarist said:

Hi @JoeQ

Down the rabbit hole!

Iron used by plants comes in two forms, ferrous (Fe2+) or ferric (Fe3+).  Plants can absorb iron (ferrous or ferric) either through the roots (both types) or through the leaves (ferrous only).  Most herbaceous plants utilize iron in the ferrous (Fe2+) state for various internal processes.

Plants utilize iron in the ferrous (Fe2+) state however the Fe2+ ion is not very stable and will rapidly oxidize into a ferric (Fe3+) ion state.  Iron the the ferric state can be utilized by plants as well but first must be converted to the ferrous state.  This is done in the root zone where various biological processes can convert ferric ions into usable ferrous ions.

EDTA chelated iron is a molecule of the ferric (Fe3+) iron bonded to a chelate molecule.  This allows the ferric iron to be utilized by plants in the root zone where the chelate molecule is 'stripped' from the ferric molecule.  Then the biological process can convert the ferric ion into usable ferrous ions. 

Unfortunately the bond between the EDTA chelate molecule and the ferric (Fe3+) iron is not very strong.  The chart below shows the effect of increasing pH and the 'breaking' of the chelate - ferric iron bond.  When the bond is broken the ferric molecule is free to bond with any other available molecule, typically oxygen.  This forms a precipitate of ferric hydroxide (insoluble particles) that can indeed be visible.  Hope this helps! -Roy
 

I probably could have worded my question diffrent. I'm aware of the diffrent types of Iron supplements added to the water column, and the interaction with crushed coral mentioned above. My followup was more aimed at the interaction of a root source of iron (Mexican potting clay) and if there was any mal-absourbition issues inside the plant on account of the Crushed coral.

EDIT: I would expect there would not be any ion interaction since the Crushed Coral would be in the water column and the iron source being in the substrate. 

Edited August 16, 2022 by JoeQ
Added edit to clarify post

[Anjum]

On 8/16/2022 at 12:05 AM, nabokovfan87 said:

Is there a database of PH that plants like? Maybe this is something useful for ACO to have in their website or something we can compile for ACO plants as an "advanced planted tank" tool?  The biggest one that stands out to me is how many people struggle with Scarlet Temple.

Oh good, cuz I just bought a Scarlet Temple 😅 And I've been having issues in my 29g, water wisteria is yellowing & all of the Java fern is looking rough. There was no nitrate last time I tested, figured it's just that & I need to get regular about dosing Easy Green. But I've also been trying to make sure I keep my KH up because I almost crashed a tank earlier this year. Guess I need to break out the master test kit & figure out exactly where my pH is at. 

A plant database would be helpful, listing any species specific nutrient & parameter needs (like how Java fern needs extra Potassium? Or Phosphorus? I can't remember). I would assume like terrestrial plants, the great majority prefer somewhat acidic conditions & very few prefer or tolerate alkaline. 

On 8/16/2022 at 5:54 AM, JoeQ said:

 My question now is it Iron from the water column only,  or does CC affect absorbing Iron through roots in the substrate?

I wonder this too. I would assume that in an aquarium setting, since the substrate is saturated with the water, the pH is roughly the same. But I don't know that for fact. And following the same logic, nutrients from the water would be available in the root zone. But we know that's not 100% the case, as that's why root feeders need nutrient rich substrate or root tabs. So maybe there's not a lot of mixing of open water column parameters & substrate parameters???? Down the rabbit hole indeed! 

It would appear all of this would be moot if we were using EDDHA iron, as it's unaffected by pH. But maybe there's a reason that won't work in an aquarium? 

[Seattle_Aquarist]

On 8/16/2022 at 10:01 AM, JoeQ said:

I probably could have worded my question diffrent. I'm aware of the diffrent types of Iron supplements added to the water column, and the interaction with crushed coral mentioned above. My followup was more aimed at the interaction of a root source of iron (Mexican potting clay) and if there was any mal-absourbition issues inside the plant on account of the Crushed coral.

EDIT: I would expect there would not be any ion interaction since the Crushed Coral would be in the water column and the iron source being in the substrate. 

Hi @JoeQ

Also a good question, there have been several studies but basically:

Quote

How does pH affect iron availability?

 

Iron is abundant in most soils, but as with other micro-nutrients, its availability is greatly influenced by soil conditions. Soil pH is one characteristic that has a considerable influence. Iron availability is lowest between pH 7.5 and 8.5. It becomes more available as soil pH de- creases.

Quote

What is the relationship of pH with active Fe?

 

Solubility of Fe decreases by approximately 1000-fold for each unit increase of soil pH in the range of 4–9 compared to approximately 100-fold decreases in activity of Mn, Cu, and Zn (Lindsay, 1979).

So in short yes, the pH of a tank (including the substrate) will effect the uptake of all types of iron - but ETDA chelated iron will be the most effected. -Roy