Some people in the thread below and in PMs asked about how to use Dolomite as a source of Ca and Mg.
First off - the use of Dolomite is not something you should consider to be a "magic wand" to solve problems. There isn't a single such factor in a planted tank. They all work together, as simple as that. The real challenge is to find out HOW everything works together inside the glass box, not on paper/screen. So far, 15 years into the US internet hobby, we can't say we have made great progress in answering that question.
Lately, there has been more and more interest in keeping the fertilization of a planted tank to a minimum while still being able to grow healthy plants. The fact that the Japanese company ADA has been doing that forever is another topic. The use of Dolomite is exactly along the lines of adding the least needed - it does not add Chloride, Sulphur, Potassium, or extra microelements as practically all popular water column fertilizers do.
So using Dolomite is a way to avoid accumulation of unneeded substances. Some people have started to suspect that accumulation of nitrients (especially micros) is a much greater problem than we all think. Big regular water changes do not solve that problem despite calculations that show they will. At the end - the use of "clean" sources of nutrients, that do not add additional elements is a better practice overall.
There is also a German line of fertilizers that includes products supplied in forms that have proven to be more effective (Aqua Rebel). Dolomite too has an interesting effect on plants that is beyond just supplying Ca and Mg. Dolomite solubilizes gradually and this process maybe what makes it different and more effective. Meaning that Mg from Epsom Salt (MgSO4) for example will supply Mg but the way this Mg is supplied appears to be inferior to using Dolomite. Not to mention the addition of S, which is an example of an unneeded element added along with the Mg and never tested for.
Ok. So if you have decided to give Dolomite a try here's what you need to know:
1. I use Dolomite powder made by KAL.
Someone asked why I use powder and not Dolomite pebbles which will dissolve even slower. You can find Dolomite gravel by road construction sites - it is used as a base under concrete and asphalt. But powder is way easier to measure. Dolomite does not dissolve immediately in water but it does dissolve pretty quickly. A 1" rock will be an overkill in a 100 gallon tank. Below you will see actual calculations and will agree that powder is the way to go.
2. Dolomite will supply more Ca than Mg.
That is an important detail. Using Dolomite or not your goal should be to maintain a Ca:Mg ratio of 3-4:1. Adjusting your actual ratio to that 4:1 ratio can not be done with Dolomite alone. That will be described in details below.
3. To adjust the Ca:Mg ratio in a "clean" way, not adding anything extra that will accumulate in the tank we use:
- To raise Ca - Dolomite (aslo raises Mg but less than Ca)
- To raise Mg - MgCO3.
4. Both Dolomite and MgCO3 increase GH and KH.
This certainly appears like a big problem but it isn't. Once the Ca:Mg ratio is adjusted so little Dolomite is used that the GH and KH are easily adjusted to whatever value you want them to be. As we all know ideally a planted tank should have KH of 2-4 and GH of no more than 5.
So: We use MgCO3 to add Mg and Dolomite to add Ca until we adjust the Ca:Mg ratio to 3-4:1 This is done gradually. Do not add enough Dolomite to adjust your Ca:Mg ratio in big steps. Everything in a planted tank must be done gradually and Dolomite and MgCO3 are no exception. It will take weeks to adjust the Ca:Mg ratio in a tank that has a GH of 10 and 100 ppm Ca. Keep that in mind, it's important.
Once we have the Ca:Mg right and the KH and GH more or less in line we add mainly Dolomite (+very little if any MgCO3 if needed). Fine tuning KH and GH is done, once again, with small and frequent water changes (every 3 days, 10-15%).
I use the calculators on the German website FlowGrow.de
Go to the link below:
Ca:Mg Berechnung - Flowgrow Datenbank
Make sure that the radio button "Magnesium bestimmen" is selected.
First we will enter numbers that give us a good Ca:Mg ratio:
Enter GH=7 and Ca=34. They result in a good Ca:Mg ratio.
Enter 7 for "Gesamthärte (GH)".
Enter 34 for "Referenzwert"
Click the green button "Berechnen".
The result is displayed in a white box to the right: We have 9.76 mg/L Mg (mg/L is equal to ppm). And the Ca:Mg ratio is 3.48:1.
Your real Ca:Mg ratio is off:
In this example the water test showed GH=4 and Ca=34 ppm. From example of the perfect tank above you can already tell that 34 ppm of Ca should be paired with GH=7 to have a good Ca:Mg ratio. In other words the Ca is too much for the GH of 4.
Enter 4 for "Gesamthärte (GH)".
Enter 34 for "Referenzwert".
Click the green button "Berechnen".
The result is displayed in a white box to the right: You have -3.31mg/L Mg. And the Ca:Mg ratio is negative also. This means that the Ca is way too much. So you need to increase the Mg.
Increasing the Mg:
-->How much Mg do we need to add to get to the good ratio of 4:1 Ca:Mg?
Look at the amount of Mg: it is -3.31. You want it to be 9.76 (like in the "Good" Ca:Mg ratio" example. So you need to add enough MgCO3 to increase the Mg to 9.76. Note - we are adding MgCO3. Not Dolomite!
You are starting from -3.31 and you need to get to 9.76. So you need to add about -3.31 + 9.76 = 13 ppm Mg.
We will use a 65 gallon tank as an example.
How much MgCO3 we need to add to a 65 gallon tank so we add 13 ppm of Mg?
Go to this page:
Dosierberechnung - Flowgrow Datenbank
65 gallons is roughly 200 liters. Enter 200 in the "Beckenvolumen" box. This is approximate but will work. From what I have seen 200 is a good approximation.
Ignore the "Zugabeintervall" box below "Beckenvolumen".
Under "Nahrstoff" find the drop box "Magnesium (Mg)". Leave it as it is.
In the drop box to the right of ""Magnesium (Mg)" choose "Magnesiumcarbonat MgCO3".
Enter 10 in the box that has a "g" on the right. The "g" is for "grams".
Click the green button "Berechnen" (not "Loshen" which deletes this row of drop downs).
The results are shown in a table under the green button "Berechnen in a table named "Ergebnis". The table now shows how much of what element you added with your 10 grams of MgCO3. In this case it is 14.41 mg/L (=ppm).
Now scroll below that table and look at the two white boxes below. They show how the KH and GH are affected by the addition of 10 g. of MgCO3. In this case KH was raised by 3.32 and also GH was raised by 3.32.
That means that we adjusted the GH to 7 (like the "Good" tank in the beginning of our example) and the Ca:Mg ratio should be good. But your starting KH of 4 may now read 7. That is not high but it is something to expect when we test next week. From my experience, on my tanks, the KH will actually jump only to about 6 max.
Note that other than Mg there are no extra chemical elements added. But if you use the usual source of Mg - Epsom Salt - and select it as"MgSO4.7H2O Bittersalz" you will see that it adds Mg and Sulfur. There is no need for the Sulfur. Or is there? Nobody can really tell you. If you add Epsom Salt to your tank to raise the Mg you are also constantly building the S. And never testing for it. Toxicity may happen and you don't realize why.
If you followed the above steps you should now know how to adjust your Ca:Mg ratio using MgCO3. But this thread was about Dolomite.
As you understand - if we try to adjust the Ca:Mg ratio adding Dolomite we will end up with raising the Ca, but also the GH and the Mg. We can use another source of Ca - like CaCl2 - but in this case we will be adding Chloride to the tank. Not the best idea if we strive for the least accumulation of anything. So the calculations say that by adding Dolomite we will be increasing the Mg and never get away from adding more Ca than Mg. That is why we use MgCO3 first to get the Ca:Mg ratio right with a "clean" source of Mg. Then we use Dolomite to maintain that ratio. Once again - think of the Dolomite as a source of Ca+Mg and the MgCO3 as a source of Mg.
To reiterate - this thread is about using alternative, clean, sources of the nutrients that the plants need AND about supplying them in a form that has proven to be very efficient. This thread is not about right vs. wrong.
An experience from real life: For one of my tanks adding the calculated dose of Dolomite ended up in a good Ca:Mg ratio in about 4-5 days because the plants where consuming the Mg very fast. That is not that strange - after all Mg is part of the Chlorophyll molecule. But the rate of consumption of Mg in that particular tank was extremely fast. After about 10 days the plants were growing very strong and very fast but the consumption of Mg slowed down considerably. That doesn't make much sense but apparently the plants were ramping up for great growth and needed extra Mg before the home run and less Mg during fast growth.
That example shows that the calculations would not predict what the Ca:Mg ratio would be after 4-5 days because the plants maybe in a state that requires more or less Mg. It goes without saying that the same applies for any other nutrient. Frequent testing and careful fertilization maybe an obvious solution. But it is many times better to setup the tank in such a way that fluctuations are not excessive.
For testing GH, KH, Ca, and calculating Mg precisely I use an $100 test kit made by Hach. Cheap test kits sold in fish stores will throw you off. If you tried the calculations above with different values you will see how hard it is to get the Ca:Mg ratio right. Small changes in Gh or Ca change the ratio too much. Play with the values of GH and/or Ca in the calculator below. Look how the Ca:Mg ratio changes in the white box to the right ("Ca:Mg Verhaltnis"). It's pretty tricky to get it between 3-4:1.
Ca:Mg Berechnung - Flowgrow Datenbank
So a good test kit is a must.
Hardness (Total & Calcium) Test Kit, Model HA-4P MG-L | Hach USA - Overview | Hach