when it comes to issues like this,
Flush, make sure your ph pen is calibrated, feed at half strength until the situation resolves itself.
I think 5.6 doesn't give you enough wiggle room in terms of ph sensor calibration and ph fluctuations due to various things.
5.8 is the optimal ph for soiless and hydroponic mediums.
@ jinn
That is m/l what I've been doing which is why they look light green, although I thought the optimum PH for soilless is mid-5's. That could explain some of it. I'll bump the PH up a couple of tenths. My meter is calibrated.