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Looks like nutrient issues. Possibly due to pH. Kind of need to know more. What kind of water? What nutrients? Strength? What is the pH?

pH varies between 5.5 and 6.0 I'm using RO water.

I prepared the nutrient solution myself, according to a formula I got from the website of Howard Resh.

N 180 ppm
P 50
K 210
Ca 190
Mg 45
Fe 4
B .5
Mn .5
Zn .1
Cu .1
Mo .05

EC is about 2.1

The solution tends to get too acidic and I adjust pH using NaCl every day. It's the first time I'm trying this formula.

It is hot, like 30 degrees celcius midday. The solution is about 30 degrees also. Relative Humidity about 60-70 percent.

Hi agean
The most likely cause is nutrient burn. Your EC is too high with 2.1 at these temperatures. Switch to 1.2 (increasing gradually to 1.5 with maturity of plants) it is much more appropriate for your climate . You may even run your system on 0.5 for a few days, to "cure" your plants.

DO NOT use NaCl as a pH up - The high Chlorine may be an annex cause of your problem, - depending on how much you use, it may even be the main cause.

I recommend to lower P content to 35 ppm, it is sufficient and will prevent the solution from moving to acidic. 35 ppm of Magnesium is sufficient as well and 2 ppm of Fe more than sufficient. The lower EC also will prevent your solution to go acidic. If you use both, lower Phosphorus and (much) lower EC, your solution will most probably be stable or having a tendency to raise in pH, which is the more typical effect.

PS: 30C for outside and nutrient PEAKS is not exactly ideal and you should not exceed these - but it's what most farms here around grow lettuce at and cope with, ours included. As long as your roots look fine and there is no appearance of Phytophthora sp. you shall be OK to bordereline under these conditions.

BtW: the modified formula (less P, Mg and Fe) I gave you here, is what farmers widely use successfully in sub-tropical climate of the region. It has proved to be balanced and adequate for years.

Hello Lucas,

Thank you very much for the help. I will lower Mg, Fe and P as you suggest.

There is one thing I don't understand. When I prepare the solution according to these ppms, I get an EC of 2.1. With lowered P, Mg and Fe concentration it will be lower but probably still be higher than 1.2. If I lower EC by diluting the solution, then I'll have lower ppms. So what do I do?

I'm using these fertilizers to prepare the solution:

ammonium nitrate
calcium nitrate
potassium nitrate
potassium mono phospate
potassium sulfate
magnesium sulfate
iron EDTA
boric acid
manganese sulfate
zinc sulfate
copper sulfate
sodium molybdate

And I am using RO water.

Do you have any suggestions about NH3/NH4 ratio?

Also, what do you recommend to use as pH up and down?

Thanks again.

Hi again aegean,

Yes, any such formulation will end up in a specific EC, as in 2.0 or 2.1. This is in fact the approximate outcome for a number of formulations. But at this level you have to understand that we have got two valid perspectives and options. Firstly, the total (original) concentration of such formula - and secondly a certain dilution factor of the same formula. The actual EC of a formula (as in 2.1 mS/cm) doesn't necessary mean that it is the only valid concentration or dilution rate we may use.

It's a bit confusing, as one may indeed think that the formula is calculated to give us exactly the necessary ppm for each element, and that less would obviously not be sufficient. But it's actually not like that - as such formula is rather generous with each elemental ppm and thus reflects more like the profile of a maximal concentration. If you like, such formulation includes the possibility of a certain/higher dilution factor. And here, less can indeed be more (appropriate).

In fact, the practically applied EC needs to be adopted to the growing conditions and climate, the size/maturity- and the resulting evapo-transpiration of the plants. Generally this means the higher the nutrient consumption, the lower the EC. And, the smaller he plants the lower as well. Actually lowering the EC in the first case, is to keep it most stable (not climbing due to high evaporation or e-transpiration) in the Nutrient solution.

Making a long story short: what do you do? You lower the EC and don't worry about sufficiency - with this formula at 1.2-1.5 it's just fine for lettuce.

About NH3/NH4 ratios?
Well that's a question of 1000 points. Because the NH3/NH4 ratio in a nutrient solution will affect pH and it's fluctuations greatly. A nutrient solution that only provides NH3 nitrogen tends to increase solution pH, while with the use of approximately 10%-20% of the total nitrogen as NH4+, the nutrient solution pH is likely to stabilise under pH 6. (theoretically at around 5.5) But a disproportion of Ammonium nitrate may reduce calcium uptake as well. And, if you use a system that promotes bacterial activity, with buckets and/or bigger amounts of medium, -or even if there is build up of larger root systems eventually, bacterial activity can transform NH4 into NH3.

Last but not least, you have to consider that not only ammonium nitrate provides the NH4 part of the nitrogen, calcium nitrate also/already has 1.3 parts of NH4 to 15.6 parts of NH3.

Making another long story short, you may actually reduce or experiment with the NH4 part (provided by ammonium nitrate ) to stabilise your nutrient's PH. As your pH tends to fall, you would reduce the NH4 part from 15 to 10 % (for example). But please consider that IF you already have reduced P and your nutrient concentration (EC) - all of it will affect pH! You shall only chose one option or transformation at a time, to observe changes.

As for a recommendation of any pH-up or down, there is no actual recommendation from my side, except the classical acids and bases in use.
I would rather try (as you have got the possibility) to achieve pH buffering and stability with a balanced content of potassium mono phosphate and ammonium part of N. Even with a little swing until the next nutrient change or top-off, you and your plants are better off without any use of ph-up or down.

In case you can't achieve enough pH stability with transforming the formula, reduce- or leave out more of the NH4, provided by ammonium nitrate. As a result your solution pH will have the tendency to raise. Then reduce N (provided by calcium nitrate) by about 20-30 ppm and adjust pH with nitric acid (which will provide some N). Be careful though, as this acid (when coming in usually high concentrations) burns holes through reinforced concrete and/or your hands! Alternatively Sulphuric acid (diluted) may do the trick as well and as you have reduced Mg/S already, no need to change your formula any further. The supplemental S will do no harm as long as it doesn't exceed a total of 300 ppm in your NS.

It may sound complicated, but it doesn't necessarily need to be. You may even be lucky and with the previous suggestion (of lower p) and reducing the ammonium part a bit, (by 5%) you may end-up with a pretty stable pH and little fluctuation, that doesn't actually need any further pH manipulation until next toping off or change. ;-)

Good hand and luck with that!
Cheers.

Lucas

Thank you Lucas, for this enlightening answer.

Seems like you're a professional. Are you doing hydroponics business, I mean commercially?

I ordered the book "Hydroponic Lettuce Production" by Lynette Morgan, and I hope to have it this week. This is the only one I could find on the subject, hdroponic lettuce. Do you know others that could be helpful to me?

I am an amateur but I am planning to turn it into a commercial operation. Hydroponics is very new here in Turkey, with lots of potential. I am looking for any help/info/resource that I can get.