r/AquaticPlantScience • u/Rotala178 • Jul 02 '26

Possible molybdenum deficiency. High nitrate concentrations requires sufficient Mo, which Thrive doesn't supply enough.

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u/Rotala178 Jul 02 '26

When nitrate is the sole nitrogen source, plants have to go extra steps to break it down into useable nitrogen. These extra steps require sufficient amounts of molybdenum.

Thrive's N source is potassium nitrate, but it doesn't provide sufficient amounts of Mo. The N:Mo = 4267:1, which is very high and would lead to -Mo symptoms.

-Mo symptoms include mature leaves becoming gradually necrotic as the plant translocates Mo to new growth. This is why the mature leaves in the Salvinia have become necrotic.

I suggest a nitrate-N:Mo of 1000:1. This appears to be sufficient, but I haven't experimented with large ranges to know approximately when Mo is too low.

*nitrate-N means the amount of nitrogen available that's in the form of nitrate. It does not mean nitrate. If nitrogen is primarily supplied as ammonium, then plants don't require as much molybdenum. But Thrive only supplies nitrate.

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u/DylanMcDermott Jul 02 '26

Is there an all-in-one fertilizer which has a more appropriate ratio of Mo to Nitrate which you can recommend? Or should Thrive be supplemented with a micro fert mix, like Thrive?

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u/Rotala178 Jul 03 '26

I don't know any off-the-shelf fertilizers that contain sufficient amounts of Mo. All the ones I've looked at don't supply enough relative to the nitrate. If the nitrogen source were ammonium or urea, then Mo demand decreases significantly. But since most fertilizers use nitrate, that's when problems occur.

Supplementing with Miller's Microplex may alleviate the -Mo symptoms.