2nd grow: indoor autos RQS/Barneys/FB

Day 44: Well i was out of town for 3 Days and when i came back the plants stood dry and only the crystal meth showed some clear yellowing. Over two days the other two starting to develop the same issue. I fed them on the next day with 2l nutewater for each of them, but it didn't slow the chlorosis down. I always measure PH before every watering and it is usually between 6.3 and 6.7. I don't have a clean watering routine but the get water every 2-3 days. I also have fabric pots, so i don't think they are overwatered. I can't find any pests. Kinda bamboozled about this developement. Anybody a good idea what i am missing? I will test the runoff next time i water.