The Planted Tank Forum - View Single Post - Potassium reference solution
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post #2 of (permalink) Old 07-12-2016, 10:03 PM
Solcielo lawrencia
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It's a trace toxicity, most likely iron. If the lower and middle leaves show loss of color along with the necrotic lesions and holes, then this strongly indicates iron tox. Iron and the other metals are not needed in the amounts most people think plants need, not even 0.1mg/L of Fe per week which is beyond excessive. Most of it will accumulate, damage cells and impair photosynthesis. If you've been dosing like this for at least several months, and the substrate is high CEC, and only recently had this become an issue, then the soil's adsorption capacity has been reached and all the metals dosed will be in the water column causing problems. The soil is most likely toxic at this point. Maintaining a high pH will help reduce the availability of the metals on the substrate which lowers uptake and can help prevent toxicity.
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