Nutrient solution composition problem

[omerizm]

I'm having a hard time figuring out how to prepare my nutrient solution so I decided to ask for opinions. Any help is wellcome. Here it goes:

• My source water has 72 ppm ca, 30 ppm Mg and it is also high in bicarbonates.
• I am growing mainly lettuce and some other greens.
• Reagents I'm using for macros are: calcium nitrate, potassium nitrate, ammonium nitrate, phosphoric acid, nitric acid. I am not using magnesium sulphate since 30 ppm Mg is enough.
• I'm using 15% of total N as NH4.
• I'm trying to keep EC as low as possible, using a light formula for summer lettuce. Since my source water has an EC of 0,9 mS, the solution comes around 1.7 mS and it is already high for a summer crop.

Problems:

I'm adding little cal. nit. since I already have 72 ppm in source water, so I can barely reach around 100ppm N without adding too much of other elements. I can not use more ammonium nitrate bec. I don't want to raise NH4 ratio above 15%. I can not use more nitric acid bec. ph drops too much. I cannot use more potassium nitrate bec. I can not put any more K. (That is why I prefer to use phosproric acid rather than mono potassium phosphate as the P source.)

I have difficulty adding S to the solution, since I'm not using magnesium sulfate, potassium sulfate or any other suphate salts. (well I use some for micros but they are insignificant) I could use some sulphuric acid but I'm already using nitric and phosphoric acids and I can not add more bec. ph drops too much.

So far my only solution is to add some mag. sulfate to supply S, although I have enough Mg in my source water. up to 60-70 ppm Mg does not hurt the plants but It raises the EC which is something I really don't like.

Any ideas? How to supply S without raising EC even more?

Basically what I'm trying to do is to use my source water as it is. If I can not make do with it, I'll have to install a RO unit and dilute it, but it is costly. I can not use rain water or any other water source.

Thanks.

[GpsFrontier]

Hello omerizm,
To be honest I don't know how you can add minerals to water, and not raise the EC. How much water are you needing? Can you dilute your source water with bottle distilled? You can also create your own water filtration system cheaper than buying a RO system. The cartridges run between $8 and $15 ea, and the cartridge canisters $20 ea (they hold the replaceable cartridges). You can even get inline some inline filters, like for the water line to the ice maker on the refrigerator, or patio misting systems etc. etc.. But I do know of a free nutrient calculator that might be able to help figure things out.

HydroBuddy v1.40 : The First Free Open Source Hydroponic Nutrient Calculator Program Available Online) | Science in Hydroponics

[omerizm]

I need tons of water, so bottles are not an option. Thanks for the program. I wrote a simple excel sheet that does the job but this is definitely prettier and more functional.

[GpsFrontier]

No problem, the person that created that nutrient calculator is a chemist, so you may try contacting Daniel from the blog, and asking the the question their as well.