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I have a cucumber plant that the leaves are turning yellow and the edges are drying out and dying. I thought at first that it was an iron deficiency but it's the whole leaf is blotchy yellow. I talked with a local garden center and she said it sounds like a magnesium deficiency and give it magnesium sulfate (Epsom salt). I also went to Youtube and it looks like it could be just that. My question is how much Epsom salt should I use? Should I make a foliar spray? How much Epsom salt per Gallon without hurting my fish? 

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Try these videos. If I remember there's more discussion on how much to use in the comments after the Epsom salt video. You should watch all his vids. That's where I get my education.

https://www.youtube.com/watch?v=mP_ttpjVC1o

https://www.youtube.com/watch?v=qfeZaofFK30

57.5 grams of Epsom salt into 100 US Gallons of water will garner you 15ppm of Magnesium.

15ppm is about half (30ppm) of the total Mg you would want in solution. So it's a pretty low dose and assumes there is some amount of Mg already present in your system...hence the 15ppm target (and not 30ppm)

Hope that helped.

Here's an old thread (one of a number) that covers adding Epsom salt to AP... http://community.theaquaponicsource.com/forum/topics/magnesium-defi...

Though from your description (leaf edge yellowing/necrosis) you might want to look into the possibility of a potassium deficiency.

Vald,

Now that you have provided the information to the amount where abouts in my system shall I add the epsom? Should it be added furthest away from the fish tank?

Vlad Jovanovic said:

57.5 grams of Epsom salt into 100 US Gallons of water will garner you 15ppm of Magnesium.

15ppm is about half (30ppm) of the total Mg you would want in solution. So it's a pretty low dose and assumes there is some amount of Mg already present in your system...hence the 15ppm target (and not 30ppm)

Hope that helped.

Here's an old thread (one of a number) that covers adding Epsom salt to AP... http://community.theaquaponicsource.com/forum/topics/magnesium-defi...

Though from your description (leaf edge yellowing/necrosis) you might want to look into the possibility of a potassium deficiency.

If you have a sump tank that would be fine. I'vs added directly to the fish tank in systems that don't have a sump, with no problems. Dissolve the Epsom in a bbucket with some top up water, and then add that water.

Good point! I didn't even think about dissolving it first.

Vlad Jovanovic said:

If you have a sump tank that would be fine. I'vs added directly to the fish tank in systems that don't have a sump, with no problems. Dissolve the Epsom in a bbucket with some top up water, and then add that water.

Here's some hydroponics nutrition information for tomatoes that I just stumbled upon from our local University of Arizona extension. http://ag.arizona.edu/hydroponictomatoes/nutritio.htm

You don't like the info I pass along, well then bye. 

Hi you guys. Thanks for the info. Vlad , you had said that I should look into the possibility of a potassium deficiency. How can I tell the difference between Magnesium deficiency and a potassium deficiency. I went on youtube to try to get answers and I'm still not sure. Can I treat for both and is there a way to easily test my water in the FT for these elements? Ho do you guys find these old threads on this site Is there a search engine for that?

Sure thing Jack. Happy to help. There is a search field (white rectangle) in the extreme upper right hand corner of your screen. It's to the right of your name and to the left of the little magnifying glass icon. It's a great tool, as there is very little that hasn't already been covered (in depth at times) at some time.

Magnesium (Mg) deficiencies are generally characterized by inter-venal chlorosis of the older leaves (never the youngest ones, that would be an iron [Fe] deficiency). Mg is mobiole within the plant, so when not enough is present in solution the plant can translocate Mg from it's old growth to the new growth. That is why an Mg deficiency makes itself manifest on older leaves and not young new ones. Fe on the other hand is NOT mobile within the plant, so when it is lacking in solution it will start to show on the youngest leaves.

The very first signs of a potassium (K) deficiency usually makes itself manifest visually by a yellowing (chlorotic) leaf margin. If allowed to progress the leaf margin margin becomes necrotic (brown and dead) while the inter-venal area begins to become effected as well, spreading towards the main veins towards the center of the leaf. Eventually, the entire leaf will die if you don't mitigate the deficiency.  

Yes, you can treat both simultaneously.

Instrumentation to check for Mg or K (potassium) can be rather expensive ($200 for the K checker), and the instruments readable range(s) may not be well suited for AP purposes.

Cucurbits (like cucumbers, squash, zucchini) are absolute Mg and K hogs, And new AP systems are often notoriously lacking in K, and depending on your source water, Mg. So you cucumber problem is actually quite a common one. 

Finally, something decent to watch on YouTube...Thanks Jeff S.

Jeff S said:

I try to send everyone to their site. Lots of good, accurate info that's easy to understand for us non-technical folk. 
 
Vlad Jovanovic said:

Finally, something decent to watch on YouTube...Thanks Jeff S.

Jeff S said:

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