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I'm very new to aquaponics. I started sometime in April and got a very basic setup. 150W HPS light, 2'x2' grow bed with expanded clay media, 2'x2'x6' grow tent, 30 gallon fish tank filled with mollies, flood and drain, 4 tomato plants and a small basil plant growing in it. 

pH - 7.4

Nitrates - very high (100+)

Amonia/Nitrites - 0

Flood/Drain - every 15 minutes

Light - on 17 hours per day

Photos attached.

I have gotten 3 tomatoes from the plants. One is much more dominant in the grow tent than the others and is about 4' tall. The dominant plant has tons of flowers, a couple small tomatoes, but all the plants show some foliage dropping and necrosis along shoots and stems. 

Any idea what is going on and how to fix it?

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One more image showing foliage damage.


In general a young system is not going to have a complete nutrient profile for fruiting plants. You may need to balance it.

"Excess nitrogen results in dark leaves, luxuriant growth, less flowers and plants that are more susceptible to disease and moisture stress. Fruit set is reduced and fruit color is poor. Ripening is delayed due to a suppression of K and Mg."

Try a foliar application of  micronized rock phosphate which can help with flowing. Also try to buffer with potassium bicarbonate. Both of these things might be deficient, but the excess nitrogen in the form of nitrates is also something you should address through reducing feeding and water changes.

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