If you are feeding at 6.3-6.5, and in a soil or soilless mix, there,s a very high likelyhood that your runoff is going to be even lower... You should be feeding at the high end of the soil range in a peat based soil, and the high end of the soilless range in a peat based soilless.
Also, beds may not allow the amount of oxygen into the root zone that a fast growing annual needs, ESPECIALLY running supplemental CO2 in the room.
You and Sn are both having a similar issue? Stands to reason; he was over-watering and the mulch paper on his pots is preventing air reaching the root zone. Aerate your soil; if that means poking holes in it, or drilling large holes in the sides of the beds, whatever- you need to get some oxygen in there!!!