Soil that started at a comfortable 6.5 will often have drifted well below 6 by the tenth week of a sativa flower, as months of feeding and salt buildup slowly acidify the mix. Lockout symptoms then appear that look like deficiencies but do not respond to more nutrients. Checking runoff pH every couple of weeks from week six is the habit recommended on
https://hazesativaseeds.com, along with a mild flush if it slides too far. Nobody bothers on an indica because the cycle ends before it matters.