No do not add anything to the pot other than PHed water because I think the problem you have is too much fertilizer in there already. Never add a single element to the pot always feed your full nutrient blend on the fertigation day and at that time add any additional elements but never exceed the limits for that element.
In order for your nutrients to be in balance the elements available to the plants need to be in the range for each nutrient below.
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Lets talk about calcium with fictitious numbers. Lets say your water starts out with 60 PPM and your base nutrients add 40 ppm but you think you need extra. The most you want to add is 40 PPM for a total of 140 PPM If you go over that you risk locking out Magnesium and Potassium.
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Now lets say you add just Cal-Mag to the pot. Elements do not mix in a medium like they would in a tank of water. They simply wash away the other elements and now they represent about 100% of what is presented to the roots and BAM a lock-out which looks like a deficiency and so you add more and then your plants really suffer
. Learn about Liebig's Law of the Minimum to help understand keeping your elements in balance.
Go to a local store and get some Kelp and Fulvic acid or humic acid ASAP This is what I use but any brand should work. You just need a tiny bit. Mix it in distilled water and add some surfactant. Waiting 6 days is a long time in an auto's life.
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What you need to learn about watering will come with practice. Here are the basic rules: Never let the soil dry out. Soil and or coco can become hydrophobic if allowed to dry. This means it repels water. This in turn will create dry pockets in the soil and roots there will die. If your soil - coco have accidentally dried out use a surfactant to help re-wet it. I like yucca powder. Don't let soil remain soggy by watering too much too often. Root rot, damping off, molds, fungus gnats and other problems start in soggy soil. When you do water water the entire pot. How to learn when to water starts before you plant the seed. Fill your container with fresh soil/coco and weigh it (heft it) this is the lightest weight and consider it a dry pot. Now slowly water until the soil/coco will no longer absorb the water and run-off begins; weigh the pot (heft it) this is the maximum water, the wettest the pot can get. The difference between wettest and driest is the maximum water weight, for ease of explanation lets just say the water weighs 20 pounds. When the pot loses 10 pounds (half of the water weight) it is time to water again. There is an art to watering.