I got some of it but I'm still missing something. I have a 1-3-4 solution that weighs 2.4 lbs the SG would be .288. So .347 ml/l would give me 100ppm with 1ppm-n, 3ppm-p, and 2ppm-k correct so far? And if I wanted 200 ppm of n I would need 20,000 ppm of solution? How did you turn 10,000 into 8ml/l. I divided 10,000 by 100 then multiplied by .08 and got 8 but when I tried that on mine I came up with 69 and that doesn't seem right. That was some heavy shit you just laid on me. I seriously just sat here since you posted with pen and paper running numbers. Im giving my brain a break for tonight but will definitely be back to this. Thank you for that. I really appreciate your time.
I just realized I may not have been clear on one thing. In regards to Specific Gravity, you have to use the correct units.
You have a liquid that weighs 2.4 lbs. Well, you don't have 1 gallon now do you? So, you have to convert. You probably have 1 quart. Is that right? or is it 1 Liter? You have to convert everything to gallons before dividing by 8.34. That 8.34 number is the density of water in lbs/gallon.
So, my mistake for not being clear on that.
Also, I'm glad I got you thinking.
Now, let me try and get this figured out.
You have a 1-3-4 solution. It weighs 2.4 lbs, presumably, a 1 quart? If it is 1L, let me know, it changes because 1L is not the same as 1 quart. Anyway, 1 gallon your solution will weigh 9.6 lbs. This is a specific gravity of 1.15. So, to add 100mg/L(0.1g/L), lets do the math.
0.1/1.15 = 0.087
You need to add 0.087g/L in order to add 100ppm of solution. In doing so means you add 1 ppm Total N, 3 ppm P2O5, and 4 ppm K2O.
Before we go any farther, I want to make a suggestion: Ditch what you're using right now.
You know how I brought up Calcium Nitrate and Magnesium Nitrate? So, those along with many other fertilizers are the basis behind what ever liquid blends you have on your shelf at home. And if you want to be precise about what you are feeding your plants, then it is best to use dry, water soluble fertilizers, that are unblended.
So, you want a 3-1-2 ratio of NPK. Awesome. That's a good ratio for vegetative growth. But, again, it doesn't tell you the concentration of NPK in your feeding solution. 300ppm N, 100ppm P2O5, 200ppm K2O is the same ratio as 3ppm N, 1ppm P2O5, and 2ppm K2O. And they are both going to perform wildly different. Basically, that second one isn't going to do shit.
To save you some effort in figuring out what is a good limit, I would start with somewhere around a 200ppm limit on N and adjust everything else to accommodate that. It will be okay to go higher, say, like 300-350ppm in your feeding solution, but lets take small steps here. No need to dive into the deep end right away. We want something that will not kill the plants and also not be so dilute as to perform poorly.
And just before we get started, something I want to bring up. Your plants can handle some pretty varied concentrations of nutrients. So, when you mix a blend, don't worry too much about being truly precise. +/- 10% is okay. So, you'll see me rounding in a lot of cases. It's because it's not necessary to carry 4 or 5 significant figures through these calculations.
Alright, lets do the following, a blend that is about 3-1-2.6, from a ratio standpoint. :
200ppm Total N
66 ppm P2O5 (29 ppm P)
160 ppm K2O (133 ppm K)
We'll also need Calcium and Magnesium.
So, lets do
90ppm Ca
40ppm Mg
I'll get to the micronutrients later.
We're going to use the following fertilizers to achieve this:
Calcium Nitrate (15.5-0-0, 19% Ca, 14.4% N-NO3, 1.1% N-NH4)
Magnesium Nitrate (11-0-0, 9.6% Mg)
Potassium Nitrate (13.7-0-46) 46% K2O = 38% K
Mono Ammonium Phosphate (MAP) (12-61-0) 61% P2O5 = 26.5% P
Ammonium Sulfate (21-0-0, 24% S)
473 mg/L of Calcium Nitrate = 90 ppm Ca, 73 ppm Total N (68 ppm N-NO3, 5 ppm N-NH4)
417 mg/L of Magnesium Nitrate = 40 ppm Mg, 46 ppm Total N (46 ppm N-NO3)
350 mg/L of Potassium Nitrate = 133 ppm K, 48 ppm Total N (48 ppm N-NO3)
109 mg/L of MAP = 29 ppm P, 13 ppm Total N (13 ppm N-NH4)
95 mg/L of Ammonium Sulfate = 23 ppm S, 20 ppm Total N (20 ppm N-NH4)
Add it up:
200 ppm Total N (162 ppm N-NO3, 38 ppm N-NH4)
29 ppm P (66 ppm P2O5)
133 ppm K (160 ppm K2O)
90 ppm Ca
40 ppm Mg
23 ppm S
Sulfur is the one I didn't give a requirement for here, as you'll note. While plants need Sulfur, it's not that important, and they can tolerate relatively high levels of it without it being detrimental. So, I always let sulfur be the wildcard while I make sure I always meet my NPKCaMg requirements.
If you want Potassium, but don't want extra Nitrogen, consider Potassium Sulfate, also called Sulfate of Potash. Also consider Potassium Carbonate and Potassium Silicate. Potassium Silicate is beneficial independently due to the silicon addition.
If you want Potassium, but also want more Phosphorus, consider Mono Potassium Phosphate, MKP. This is a common PK booster.
If you want Magnesium, but don't want extra Nitrogen, consider Magnesium Sulfate, also called Epsom Salt.
Now, coming back around to the micronutrients. I didn't list any requirements. But they are still needed, right? Just find yourself a general purpose Micro mix for hydroponics. Make sure what you feed to the plants is 1-2 ppm Fe, and everything else will fall in place.
