pH problem or is nutrients missing some trace element

16 years ago

I am just curious because I just ordered a new batch of the same fertilizer I had before (except 22lbs of it) in a 2 gal bucket. I have noticed on some of my new growth that I have some yellowing of the leaves with green veins still showing.

This is probably either an iron or magnesium deficiency. The magnesium is mine to add but the iron is supplied.

Now of course more factors come in to play. I have a heavy load of plants including peppers, tomatoes and herbs. They may be depleting some element faster than others. I have to top off my 40gal resivoir tank twice per week. I have had this new batch of fert for 1month now and I even mixed it up to ensure all was mixed evenly. Have you ever had something missing?

Now another equally realistic scenario is that I have high pH in my system. I read that high pH can inhibit the uptake of some nutrients such as iron. For some reason I can't get it down to the recommended 6.4 instread my pH stays around 8.4. I have used citric acid and vinegar to lower the pH and it does temporarily but I must use large amount.

When I say large amounts for a 55gal tank of nutrient solution I probably add say 200ml just to get the pH in the low sevens or 6's. Then the next day the pH is back into the 8's. This is nutrient solution that is in a holding tank and no plants are in it. I don't add more vinegar because I don't want to damage the plants in some way. Another factor is that I am on well water.

How much vinegar can I safely add? If the pH remains high and I keep adding acid to lower it can this harm the plants as long as the pH doesn't go too low?

Any other suggestions or methods are appreciated.

Chris

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Comments (4)

iliketoast
16 years ago
I get that on my azaleas sometimes. Iron chlorosis is your problem. You can prove it by buying a pump spray bottle (for a buck) and some azalea plant food (the blue colored water soluble kind, like "Miracle grow - Azaleas"). Mist the bottom of the leaves on your plants with a half strength solution (1.5 tsp/gallon), and you'll see results in 2 days, no matter what the pH is in your nutrient solution.

The pH HAS to come down. If you're softening your water, I would suggest using citric acid over vinegar. But only because softened water + vinegar = sodium acetate. That stuff makes my eyes sting. I have no idea what it does to plants :(.
greystoke
16 years ago
If your tap water has such a high pH, then is has a large amount of calcium/magnesium bicarbonate in solution. That stuff is a strong pH buffer which makes it difficult to get it down.
I would suggest to prepare the water in a container with an aquarium aerator (bubbler) in it and let the water settle, while - at the same time - bringing the pH down gradually with vinegar or citric acid. The bicarbs will then be transformed into Ca/Mg-acetate and CO2 gas which will be driven off by the bubbler.
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norm34
16 years ago
I suspect that high PH is the basis of your problem and iron shortage becomes the first casuality.
There are a couple things you can try. Chleated minors added to the nutrient tank might solve the problem. They can be picked up with a higher PH than standard minors.

Phosphoric acid is a far better choice to bring down the PH. I am not sure what part of the state you live in but I buy phosphoric acid at Southern Agriculture which is located north of Palmetto. Their prices are very reasonable.

Another choice is adding a small amount of ammonium nitrate. This lowers the PH as it is used. This needs to be done with care because too much nitrogen can cause problems.
You can probably use up to 15% of your nitrogen with problems.
tclynx
16 years ago
Definitely a pH problem with the iron uptake. People doing Aquaponics use cleated Iron since for the fish/bacteria involved in AP wants a pH closer to 7 or a bit above.

The problems with vinegar and citric acid is that they break down pretty quickly allowing the pH to bounce (which is hard on plants.) The Phosphoric acid is a better choice but if you don't want to have to regularly add acid to the system, you might be better off using the softened water or rain water in your system. I had trouble with keeping my pH low enough untill I switched to collecting rain water for the hydroponics.

On a side note, some media tends to bring the pH down so if you want to use something like cypress mulch or coco coir fiber, a high pH water might be good to counteract the media.

Here is a link that might be useful: My Hydro Page