Totally too soft source water. You MUST add calmag up to 250 ppm, and THEN use a coco nute. That's calcium def right there. If your nute is not a coco nute, add it up to 300ppm instead. Coco scavenges calcium.
Also, with coco + perlite, it is super hard to over water. But in grow bags, it is hard to do the lift test- you should not get in the habit of moving grow bags around! They jostle the roots and can damage them.