- Thread starter musa
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your help is much appreciated! I tried that, as you mentioned it to me on a similar problem. I gave it once a high dose of epsom salt in water (300 µS) and twice a small amount with my regular fertilizer. But on the gigantifolium there was no recognizable effect. I hope the dosage was ok?

That’s really not a very high dose. My understanding is that Epsom Salts adds about 7µS/cm per ppm Mg, so your 300µS dosing was about 43 ppm Mg, which falls in the range of recommended level for someone feeding 100 ppm N weekly (30-60% of the N).

your help is much appreciated! I tried that, as you mentioned it to me on a similar problem. I gave it once a high dose of epsom salt in water (300 µS) and twice a small amount with my regular fertilizer. But on the gigantifolium there was no recognizable effect. I hope the dosage was ok?

so I'll give some more. What would you suggest? Above you mentioned 1-2 ml MgSO4 solution per liter. As I have Epsom Salt as powder how much would that be in mg?

As for the calculations I'm completly stuck. 1 ppm of Epsom Salt = 7 µS. Is Epsom Salt so very different from other salts, as I found several tables and calculators which give different figures. e.g. this calculator says 1 ppm = 1,56 µS without explicitly refering to MgSO4. How is that possible?

Sorry for all that confusion, but I'm no chemist at all and I try to get it right. I hope you won't get mad at me...

It's not. There is simply no way it can give a reasonable solute concentration, because different ions have different conductivities for the same ppm concentration and they can change when in combination.this calculator says 1 ppm = 1,56 µS without explicitly refering to MgSO4. How is that possible?

The best way I know to demonstrate that is by comparing MSU WW, MSU RO, and K-Lite, three fertilizers made up of the very same ingredients, and look at the normalized values (normalized to the MSU WW):

► For a 100 ppm N solution the RO has an EC that is 18% higher than the WW formula, while the K-Lite is only 4% higher.

► The True TDS of the RO formula is 40% greater and K-Lite 45% than that of the WW formula.

The calculator you linked to, when using the EC's provided by the manufacturer (the first row), would give TDS values of 435, 512, and 454 ppm, respectively, so would under-report them by 20%, 31% and 41%.

The number I was given by a professional in plant nutrition was that Epsom Salts (MgSO4-7H2O) provides about 7µS/cm per ppm Mg. I recently read another article that said 7.6, but that's close enough either way.

From a practical perspective, anywhere from 1/8-1/4 tsp/gal weekly, or 1/2-1 tsp/gal monthly is fine.

I hope I got the calculations right in accordance with my equippement.

To get 1/2 tsp per gal I put 1/4 tsp (~ 1.2 ml) in 2 l. That is on my scale ~1700 mg Epsom Salt per 2 liters of water. As I understand it that would be 850 ppm.

My EC-meter shows an augmentation of 700 µS.

The values still don't fit, but maybe my scale or EC-meter are out of order.

I'll try that today and report on the effect.