# [APD] Ca/Mg ratios

The GH in my water is naturally <.5 dGH. I am using CaCO3 and MgSO4 to raise the GH to 5.

1. What is the recommended ratio of Ca to Mg?

2. Is it correct to say that if I have 1 degree of GH =from Ca. and 1 from Mg, that I have a total GH of 2?

2. I found in a posting on the Krib from Paul Sears on 7/7/98 containing this info:
1 GH is 0.179 x 40 ppm Ca++ = 7.2 ppm Ca++
1 GH is 0.179 x 24 ppm Mg++ = 4.3 ppm Mg++
(for the whole posting, see http://www.thekrib.com/Plants/CO2/units.html)

Using Chuck Gadd's calculator, I calculate that 1 tablespoon of MgSO4 adds 7.06 ppm Mg, which is close enough to 7.2 for my taste, given the uncertainty of the amount of water in the tank.

I also know that 1 tsp CaCO3 in 26g will raise the GH 1 degree, so 2.25t will raise it approximately 1 degree in my tank.

So once I know the ratio of Ca:Mg, I should be able to figure out how much of each to add to my fishtank for the plants to be in GH nirvana, yes?

I am changing the water in my tank RIGHT NOW, so quick response would be great!

```Thanks,
Rachel```

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