I gave them a 3ml dose of cal-mag, once last week, and a 2ml dose last night. I have been thinking phosphate too, So last night I added 2ml of Tiger Bloom also. I prefer to grow organic, but sometimes if it needs an immediate fix, I cheat and pull out the chemicals.Nothing wrong with 6.7 ph , with out knowing the soil and the nutrients you are using , I would learn to phosphate deficiency , but in saying that how often have you been giving Cal Mag .
The soil is Espoma, a pretty common national brand name. But its not a super soil.