Benefits of crushed coral?

[Evan Baker]

I'm aware of the overall benefits of crushed coral to raise PH and so forth.  But I have heard Cory state they use it in the warehouse with the live plants.  I don't understand the specific benefits of raised PH and such with live plants.  Can someone educate me on this please?

[Mmiller2001]

There's no benefit but for a few select plants.

[K McZongo]

Yup, it's a nice tool for those of us with really soft water/low ph.  Its probably more useful for fish/shrimp rather than plants.

[Seattle_Aquarist]

On 9/24/2022 at 3:41 PM, Evan Baker said:

I'm aware of the overall benefits of crushed coral to raise PH and so forth.  But I have heard Cory state they use it in the warehouse with the live plants.  I don't understand the specific benefits of raised PH and such with live plants.  Can someone educate me on this please?

Hi @Evan Baker

Calcium (Ca) and magnesium (Mg) along with iron (Fe) are considered 'Secondary Nutrients' as opposed to the Primary Nutrients nitrogen (N), potassium (K), and phosphorus (aka phosphate; P).  All of the nutrients are needed by plants for healthy growth.  Some plants need more of some nutrients than others but for healthy plant  growth they are all needed to some degree.

The problems can start to occur if there is too little or too much of a particular nutrient.  If there is too little of a nutrient then growth is effected and we say a deficiency has occurred.  But what if there is too much of a nutrient?  Studies have been made, most notably by D. Mulder in the early 1950's, about nutrient interactions and how too much a nutrient to effect the uptake of another nutrient by a plant.  The trick is basically not to end up with an excessively high about of any nutrient.  Typically it has been found that maintaining a calcium to magnesium ration of 3:1 - 4:1 is good for our plants.  Seachem Equilibrium is about 3.3:1 Ca:Mg ration.  When one of the other becomes too great it effects the ability of a plant to uptake the other.  (See Chart)


Using coral, sea shells, limestone, which are all forms of calcium carbonate in our tanks does release the calcium that plants require however we have to way of controlling the amount of calcium that is released.  We have no way of easily insuring that we do not exceed the amount that effects plant growth negatively.  Even worse, calcium carbonate releases carbonate molecules into the water increasing the pH, in many cases well above what we want for a planted tank which is a pH that is close to neutral or slightly acidic.  Tanks with calcium carbonate added can easily have a pH or 8.0 or higher.  What is wrong with a high pH?  Some plant species will not tolerate it (as well as some fish species) but for plants a high pH can also effect the availability of nutrients. (see chart)  Manganese, phosphorus, and iron are three nutrients that plants have more trouble utilizing at a higher pH.


In conclusion, like most things in life moderation and balance are good but uncontrolled excesses can cause poor results.  -Roy