Problems with pH in hydroponics.
Joined: 12 April 2005
Topic: Problems with pH in hydroponics.
Posted: 11 April 2005 at 19:34
I have a problem with maintaining a demended pH in my grow medium. I use rockwool, pH in the excess water was about 7.0. I've flushed the slabs with plain water, pH about 5.5. After pumping ca. 150 litres pH dropped to 6.6. Should I flush them any more? And why is the pH level rising, I was told it should fall down. And second problem concerns a few plants - they have very strange syndroms. Their leaves are spotted, spots are light green (even gray) while the rest of the leave is medium green. Recently, I've watered them with too high EC water, could that be the cause? Or is this a result of high pH? Please answer quick cause plants are growing. Tanks in advance.
Joined: 13 June 2003
|Quote Reply Posted: 15 April 2005 at 11:17|
It might be a good idea not to lower your pH quite so much.
Hydro cultivation requires lower pH than soil - we usually keep hydro feed water around pH 5.7, maybe 5.6 if some cases.
But pH 5.5 is too low. This might be the cause of the discolouration in your plants' leaves.
Water that's too acidic can cause damage to the leaves, but the more common effect of pH imbalance is that plants can't make full use of the food that's available to them - which can lead to nutrient imbalance even if all the necessary nutrients are present.
Don't worry too much about the rise in pH in the runoff from your rockwool. This is quite common.
Some grow-sites say that rockwool itself raises the pH of feedwater (it's not clear whether they mean that this happens the first time you saturate the rockwool, or every time water passes through it).
I'm not sure if this is strictly accurate, but it's quite common for the pH of feed water to rise overnight. We use nitric acid (HNO2) to lower pH, which breaks down into N over time. As the acid breaks down, pH rises.
As long as you keep adding feed-water of the correct pH, your plants should be fine.
Give them nutrient water of pH 5.7 and they should improve in a week or two.
You don't mention what your EC is, but keep it below 1.5 or 1.6 if your plants are still vegetating.
Also, while flushing can help to correct pH, the main purpose of flushing is to wash out excessive build-ups of nutrient.
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