clangerot
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Hydroponic Plants Die Once They Reach 6 Inches

I am a high school science teacher and my Biology class has set up a hydroponic set up in my classroom. We have grown beans, corn, cucumber, and tomatoes from seeds. The class has successfully grown the seeds in rockwool and have transplanted the plants to they system using expaned gravel. The system uses fish excrement. The plants do great untill they get about 6 inches tall (bean) or 3 inches tall (tomatoes). The class nor me understand why they are dying. Below is the information I do know.

Ph is 7.6
Nitrate is 0 ppm
Plant lights 16 hours

*dim*
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watch this guy's videos (he is very good, and you may get some valuable advice which will help)



https://www.youtube.com/watch?feature=pl ... Yv9iu2NI3M

he has more interesting videos on his youtube site

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rainbowgardener
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I know next to nothing about hydroponics and have never done any. But do you want your nitrates at 0? I thought nitrates was how hydro grown plants got their nitrogen fertilizing. If they aren't getting enough nitrogen, they can't grow.

Also 7.6 is slightly alkaline. Probably not enough to kill your plants, but in general veggies like slightly acid.

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rainbowgardener
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I did a quick look around and it looked like folks were saying nitrate concentrations between 70 - 300 ppm and pH between 5.5 and 6.5.

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applestar
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Fish excrement -- are you growing in an aquaponics system?
If not, are you circulating the fluids (ebb and flow I think its called) or are the plants in a net/basket pot over an aerated reservoir? Or are they in a floating planter?

What kind of light set up for the plants?
What kind of temperatures in the classroom? Overnight lows?
How are you handling the differences in plant heights?

ogik
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clangerot wrote: Ph is 7.6
Nitrate is 0 ppm
Plant lights 16 hours
There is your first and most important factor which you are totally getting wrong. pH should be under 7.0 and above 5.5. so 5.5 pH - 6.8 is the range you want to aim for. Tomatoes especially love the 5.8 range. So you might be getting a nutrient lock out thus not allowing you to intake any nutrients.

Second, Nitrate is extremely important and should be anywhere in the vacinity of 200-250ppm.

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rainbowgardener
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rainbowgardener wrote:I did a quick look around and it looked like folks were saying nitrate concentrations between 70 - 300 ppm and pH between 5.5 and 6.5.



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