What deficiency is this?

[Jonathan Kadish NYC AA Chair]

Potassium? Iron? Only on a few leafs older growth. New growth is fine.

[Vlad Jovanovic]

Intervenal chlorosis on OLDER leaves (as opposed to new ones) is usually a sign of Magnesium deficiency.

A Magnesium (Mg) deficiency will look pretty much just like Iron (Fe) deficiency, EXCEPT that Iron (Fe) def will manifest itself on the newer leaves, while Magnesium (Mg) def will show on the older ones...

MgSO4 7H2O (Epsom salt) would be a good way to supplement Mg.

Some of the tip burn and necrotic lesions beginning to form might be Potassium (K) related? But you probably snapped a pic of the worst looking leaf. At any rate some Potassium BiCarbonate (KHCO3) wouldn't hurt any. It makes for a great anti-fungal foliar spray, and you can use it to buffer up your pH (and it'll add some K as well of course)... 

[Jonathan Kadish NYC AA Chair]

I was thinking Mg, i am already putting a small amount of K2SO4 in... I had some so I though that may help the Potassium.

Thanks for the tips.

[Jonathan Kadish NYC AA Chair]

With 100 liter tank how much MgSO4 would you add?

[Jonathan Kadish NYC AA Chair]

Thanks Peter... I just through in a teaspoon. I'll see what happens.

Peter Shaw said:

hydro recommendations are about 40ppm, but it really depends on your Ca concentrations.

Ca is usually about 4+ times the Mg, if you put in too much Mg you will have Ca problems.

i know this does not answer your question.

once you decide what ppm you want, you can do this: 1ppm = 1mg/L 

but, that is not 1 mg of MgS04 as Mg is only 20% of the weight.

If you use Epsom salts its closer to 10%

so, you could change the formula to 1ppm = 0.2mg/L or 1ppm = 0.1g/L of epsom salt

or you could try this..

desired ppm/75/.1 = oz of Epsom Salts/100 gallons of water

say 10ppm /75/.01 = 13 oz/100gal

then convert to grams and Liters.

If you dont know how much you need, then just "throw some in"