Magnesium carbonate as pH up

[3Berries]

I got some Magnesium Carbonate (MgCO3) to see if it works good for pH up buffer. And so far so good. It's otherwise know as chalk for weigh lifters.

First test was a gallon of 1/2 nute mix at 6.1pH. A 1/4 gram and sitting over night the pH rose to 7.4

Got three gallons of rain at 6.2 pH and added 1/2, 3/4 and 1 gram to them to see how that changes the pH. Rainwater is terribly hard to get a good pH reading on when it's got a ppm count under 20.

I have a slurry of it mixed with distilled water. Going to filter it out tomorrow and see but the clear liquid now is already at 9.7 pH.

I'm trying to avoid using potassium based pH up.

[cybersmib]

Are you using a control sample?

[3Berries]

That's what I'm doing. The water is common. I just tried the 1/2 nute mix to see what it would do. Will have to repeat after seeing how the straight water turns out.

[3Berries]

Looks like the top end buffering limit is 9.7pH.

Had three gallons of rain water at ~6.2 and 20 ppm. Added 1/2, 3/4 and1 gram to them yesterday. 1/2 gr was 9.4 this morning and the other two were 9.7. The 9.7 were a bit cloudy yet so some MgCO3 is still unreacted, hence the 9.7 Ph or buffer limit.

Today I added a 1/2 teaspoon of my Miracle Grow Bloom Buster, what I use for flowering, 10-52-10 Half strength for indoor.
I let that sit a bit and see what's it settles out to.

But I have two plants with stubbornly low pH runoff. around 5.9. Yesterday I ran rain water though one I have in veg as it was locked out for Mg apparently, 2 gallons through a 1.25 gallon container. Didn't change the pH at all. Did lower the ppm. I also have a flowering one in the same shape pH wise. Been running nothing but rain water though it.

So yesterday I pHed the water for both to 7.4 with the MgCO3 and 1/2 nute water. The run off for both was much higher at 6.3 for the veg and 6.6 for the flower. PPM was under 1000. I'll water them next with rain and see if the pH holds.

But it appears if you want to use MGCO3 for pH up it works great with very little needed. 1/4 gr or so to the gallon for a big change. It's a lightweight fluffy powder. A leveled 1/2 tsp was .33 gr.

[3Berries]

This worked great to get the pH down in the two plants I had that were below 6 after many flushes. But is basically like using limestone.


My well water is 440 ppm 90/10 Ca/Mg. So my plan for base water in the future is rain with 3 cups of well an a 1/2 gr of MgCO3 to start. This has a high pH of over 8.0 but has no lasting power. Any nutes added will bring it down or any low pH it comes into contact in the soil will react.

I've been alternating with rain and nuted water watching the run off pH and ppm count. All run off gets put to good use.