Crushed Coral vs Limestone?

[JoeQ]

Is there any advantages/disadvantages in using one over the other when trying to buffer KH only. Will using limestone buffer GH as well? 

Edited April 3, 2022 by JoeQ

[Fish Folk]

On 4/3/2022 at 8:33 AM, JoeQ said:

Is there any advantages in using one over the other when trying to buffer KH only. Will using limestone buffer GH as well? 

Good question! I am not an expert here. Others on the forum can probably help out more. I use crushed coral in some tanks, have lots of limestone in one tank, and use shells from the outer banks in a few aquariums as well.

From what I understand, crushed coral raises KH. I am not sure about it’s affect on GH. We used some, for example, on each side in this tank when breeding Auratus…

You can also see some shells, which are a much slower release.

Some while later, breeding Acaras in this same tank here, the crushed coral has dispersed around the tank substrate…

The thing is that if you’re changing a lot of water, you’re not really experiencing the results of increased KH, but more or less just resetting water with soft water again abs again. Even after adding crushed coral, our parameters read…

We used some huge pieces of Texas Holey Rock (honeycomb limestone) in one tank…

But again, with frequent water changes, I’m not sure there is much of an effect. pH stays buoyantly high… otherwise, it’s not as much of an effect as you’d think.

[JoeQ]

My water has pretty much no kh, but the gh is good at 150ppm (my lava rocks may be buffering this). I've been using crushed coral to buffer kh but im looking for better options. Particularly for a more pleasing scape, that and it allows for more objects to plant plants on. 🤣

[modified lung]

Limestone and crushed coral are both calcium carbonate so they will raise both your KH and GH over time. They both dissolve very slowly so, exactly like Fish Folk said, you probably won't notice a big difference in GH with regular water changes. CO2 injection can dissolve limestone a lot faster though which I wouldn't recommend unless you have lost of experience. 

[JoeQ]

On 4/3/2022 at 10:06 AM, modified lung said:

Limestone and crushed coral are both calcium carbonate so they will raise both your KH and GH over time. They both dissolve very slowly so, exactly like Fish Folk said, you probably won't notice a big difference in GH with regular water changes. CO2 injection can dissolve limestone a lot faster though which I wouldn't recommend unless you have lost of experience. 

Thanks, or no co2 (it's cheating) 🤣

[Seattle_Aquarist]

On 4/3/2022 at 5:33 AM, JoeQ said:

Is there any advantages/disadvantages in using one over the other when trying to buffer KH only. Will using limestone buffer GH as well? 

Hi @JoeQ

@modified lung is correct that both are calcium carbonate however there are differences one being molecular hardness.  Hardness is measured in Mohs.  The harder the material the slower it will dissolve.  Here are the Moh values for limestone, coral, and sea shells which are all forms of calcium carbonate:

Limestone - 2-4 Moh
Coral          - 3-4 Moh
Sea Shells   - 3-10 Moh

As you can see coral can be up to 50% harder than limestone on the low end and about the same on the high end.  Shells can be up to 2-1/2 times harder than limestone.

Again, I do not recommend using any of the above products in a planted tank.  Using these materials increases the pH to alkaline which makes 95% or more of the EDTA chelated iron in Easy Green unavailable to plants.  The materials above also effect the calcium : magnesium (Ca:Mg) ratio resulting in reduced plant uptake of the primary nutrient phosphorus (phosphate) and the secondary nutrient Magnesium along with some micro-nutrients resulting in plants displaying nutrient deficiencies.  Perhaps @Corywill read this thread and do something to resolve this issue first by stopping the recommendation of limestone for planted aquariums and secondly by changing the formula for Easy Green to utilize a form or iron that is more available in alkaline conditions such as DTPA or EDDHA chelated iron products.

Quote

EDTA strongly holds iron in solution up to pH 6.0, but by pH 6.5, almost one-half the iron is precipitated, and by pH 7.0, almost none of the iron is available to plants. DTPA is an excellent iron source up to media pH 7.0; however, 60 percent of the iron is precipitated and unavailable by pH 8.0. EDDHA is the strongest chelate of any of the commonly used materials and maintains iron availability to plants past pH 9.0.

If you really need to increase the carbonate hardness (dKH) (which some question the necessity of doing even with CO2 use) I recommend bicarbonate of soda / baking soda (not powder) / NaHCO₃.  1/16 teaspoon per 3 gallons will increase your dKH by about 1.0 degrees.  Remember as you increase dKH you are also increasing the pH of the tank so gradually increase the dKH or pH shock to the fish may occur. -Roy

[JoeQ]

On 4/3/2022 at 1:30 PM, Seattle_Aquarist said:

Hi @JoeQ

@modified lung is correct that both are calcium carbonate however there are differences one being molecular hardness.  Hardness is measured in Mohs.  The harder the material the slower it will dissolve.  Here are the Moh values for limestone, coral, and sea shells which are all forms of calcium carbonate:

Limestone - 2-4 Moh
Coral          - 3-4 Moh
Sea Shells   - 3-10 Moh

As you can see coral can be up to 50% harder than limestone on the low end and about the same on the high end.  Shells can be up to 2-1/2 times harder than limestone.

Again, I do not recommend using any of the above products in a planted tank.  Using these materials increases the pH to alkaline which makes 95% or more of the EDTA chelated iron in Easy Green unavailable to plants.  The materials above also effect the calcium : magnesium (Ca:Mg) ratio resulting in reduced plant uptake of the primary nutrient phosphorus (phosphate) and the secondary nutrient Magnesium along with some micro-nutrients resulting in plants displaying nutrient deficiencies.  Perhaps @Corywill read this thread and do something to resolve this issue first by stopping the recommendation of limestone for planted aquariums and secondly by changing the formula for Easy Green to utilize a form or iron that is more available in alkaline conditions such as DTPA or EDDHA chelated iron products.

If you really need to increase the carbonate hardness (dKH) (which some question the necessity of doing even with CO2 use) I recommend bicarbonate of soda / baking soda (not powder) / NaHCO₃.  1/16 teaspoon per 3 gallons will increase your dKH by about 1.0 degrees.  Remember as you increase dKH you are also increasing the pH of the tank so gradually increase the dKH or pH shock to the fish may occur. -Roy

Thanks roy, itll take me a while to digest all that. I currently do sprinkle baking soda in my tank, I started doing that last year when I had my ph bottom out from 0 kh. Over the past year or so I switched to crushed coral and I was able to get my kh to 80ppm and then started slacking on the Baking soda..... As of now my kh hovers around 40ppm even though I'm constantly adding CC which is either being bubbled out by my air stone, changed out with water changes or absorbed by plants/livestock. Its not the worst problem to have, but I wouldn't mind finding a better more reliable way to buffer! 

[modified lung]

@Seattle_Aquarist I didnt know the details of that. I'll have to write it down. Thanks!

[eatyourpeas]

On 4/3/2022 at 10:30 AM, Seattle_Aquarist said:

I recommend bicarbonate of soda / baking soda (not powder) / NaHCO₃.

I use baking soda as well. Still keep some crushed coral in some tanks, but mostly as a slow maintaining tool.