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What do you prefer to use to supplement magnesium in your ap system? Just looking around for a quick fix until I can get something more long term established...

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Thanks Vlad, it's really good to know that it is hard to screw it up :) I'll try and do the math and get back to you. I think Hydroponic Food Production has some tables and calculations I can use...

Vlad Jovanovic said:

Hey Alex, it's really doubtful that you would even get within light years of any salinity issues if you went about this in even a remotely appropriate manner. So like Rob says, don't over do it! Now, I'm not much of a fish guy, but I've shocked the hell out of some fish parasites by rapid changes in salinity (from almost zero to 4-5ppt differences) and the fish do just fine, so I'm having a hard time imagining the almost industrial quantities of Epsom salt you'd have to add to accomplish such a goof up...(You'd almost have to be trying really, really hard to fuck up on purpose)

Calculating this sort of thing by using square footage of grow space is a pretty poor way to go about this sort of thing, unless were talking about a soil garden. Percentage in solution is what you'd be after here. Shoot for an addition that results in a  15-30 ppm change. I think there is a ton of threads in the search field on how to go about that, but if you can't find any for some reason, just ask before you start adding anything and we'll go over it again here. 

Man, when it comes to algebra, I'm like former high school track star who is currently a 400 pound, middle aged old man sitting on a couch, eating potato chips while watching reruns of I Love Lucy. Not good. I need to get in shape guys. Maybe I'll start running ppm calculations on a daily basis to get my skills back....

Okay, so I've double checked my math and online information and the two match up, so I might have done something right. Here's what I got: I'll need about 12 oz. of magnesium sulfate in 600 gallons (the size of my system) for a 15ppm magnesium concentration system...sound about right?

Ok, so without referring to the all knowing internet...the ‘no algebra, no formula’s way to do this is still relatively easy. You need to know your systems total water volume in liters. 600 US gallons is 2280 (we’ll call it 2300) and we need to know that Epsom salt has a 10% Mg content…and it helps to remember that ppm is equal to mg/L…and you need to know your target ppm...

(and that in no way do you HAVE to be exact down to the gram or anything..."It's got electrolytes!!!)…

 

At 2300 liters of water…2.3 kilograms of salt would be 1ppt if only 10% of that salt is Mg that means that you’d be at 100ppm of Mg…one tenth of 2.3 kilos is 230 grams…230 grams is only 10ppm and you want 15ppm…so add half of 230 more to get 15ppm…which is 115 grams…230 grams plus 115 grams is 345 grams of Epsom salt…so 345 grams of Epsom salt into 2300 liters of water gives you 15ppm of Mg.

So converting to that mumbo-jumbo totally arbitrary imperial "system"...12 oz would be 340.1942 grams so the 'all powerful wizard of Net' was off by a bit (again all joking aside, not enough to matter)...

 

This is the pretty round about long way to arrive at this number, and there is NOTHING wrong with that at all. Just be aware that there is of coarse a very elegant and short formula to arrive at the same number (and I wrote it down on the back of Rob’s water quality lab report while sitting at the bar with him in Tuscon…so I know he knows it. I mean we really didn't drink THAT much…all things being relative and all :)



Alex Veidel said:

Man, when it comes to algebra, I'm like former high school track star who is currently a 400 pound, middle aged old man sitting on a couch, eating potato chips while watching reruns of I Love Lucy. Not good. I need to get in shape guys. Maybe I'll start running ppm calculations on a daily basis to get my skills back....

Okay, so I've double checked my math and online information and the two match up, so I might have done something right. Here's what I got: I'll need about 12 oz. of magnesium sulfate in 600 gallons (the size of my system) for a 15ppm magnesium concentration system...sound about right?

Thanks Vlad. It was good to have a brush up on my high school algebra, but I like your way better ;)

In fairness to the wizard of Net, I used a formula that calculated how many ppm of a substance you have if you dissolve a certain mass into a certain volume and just rearranged it a little. So that product was not used for it's intended purpose, and my warranty is invalid. I also did a lot of rounding, and double checked with somebody else's figures and cut them half at a glance (didn't go into decimal points) just to see if I had a ballpark answer. So my research didn't come up with 12oz of magnesiums sulfate exactly, that was just a hastily thrown together calculation.

But I recall you talking about your approach to the math before (and I recall it going completely over my head 'cause I wasn't ready for the information ;), so I'm assuming people often do what I did.

Vlad Jovanovic said:

Ok, so without referring to the all knowing internet...the ‘no algebra, no formula’s way to do this is still relatively easy. You need to know your systems total water volume in liters. 600 US gallons is 2280 (we’ll call it 2300) and we need to know that Epsom salt has a 10% Mg content…and it helps to remember that ppm is equal to mg/L…and you need to know your target ppm...

(and that in no way do you HAVE to be exact down to the gram or anything..."It's got electrolytes!!!)…

 

At 2300 liters of water…2.3 kilograms of salt would be 1ppt if only 10% of that salt is Mg that means that you’d be at 100ppm of Mg…one tenth of 2.3 kilos is 230 grams…230 grams is only 10ppm and you want 15ppm…so add half of 230 more to get 15ppm…which is 115 grams…230 grams plus 115 grams is 345 grams of Epsom salt…so 345 grams of Epsom salt into 2300 liters of water gives you 15ppm of Mg.

So converting to that mumbo-jumbo totally arbitrary imperial "system"...12 oz would be 340.1942 grams so the 'all powerful wizard of Net' was off by a bit (again all joking aside, not enough to matter)...

 

This is the pretty round about long way to arrive at this number, and there is NOTHING wrong with that at all. Just be aware that there is of coarse a very elegant and short formula to arrive at the same number (and I wrote it down on the back of Rob’s water quality lab report while sitting at the bar with him in Tuscon…so I know he knows it. I mean we really didn't drink THAT much…all things being relative and all :)

heres a great article on Mg from Maximum Yeild magazine

http://www.maximumyield.com/features/articles/item/944-miracle-myth...



Rob Nash said:

 

I have been using the cheap Iron test.. its now easy to keep it around 2.0

I usually add the Biomin Liquid Iron at the same time as the Mg

Hi Rob, Thanks for sharing your insights and experiences in AP - I always enjoy reading your posts! With regard to the above . . . what is "the cheap Iron test"? (sorry for the cockup on this post, I don't know how to properly quote someone's previous post.)

 

 

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