Quick One First Grow

Looking at your previous weeks, everything was going ok, if a little heavy on nitrogen (dark leaves) and some clawing. That the issue appeared so quick points to a combination of nute burn / lockout. What you need to do is get distilled water, enough for a thorough flush, twice the pot volume should do, so 20 liters or so, then let the plant recover without feeding for at least 1 week. As for your water source, it should have an EC / PPM of 0.4 to 0.5 EC (200 to 250 PPM), above that and it's not good for your plant, you will always risk lockouts and burns using it; below that and it needs calcium and magnesium additive. An EC / PPM meter although optional in soil, makes your life as a grower easier as it takes the guessing out of feeding. For future reference, do not feed more than once a week; feeding in soil, let the plant consume what's on the soil, only start feeding when the first signs of deficiencies appear, not before, since while a slight deficiency will not impair flowering and yield, a burn can be disastrous. Good luck