dude thats a bonafide phosphorous def, fo sho, ofcourse the tech at HG said that, because if Hand G made a cal-mag supplement he would have told you to use it, especially in an RO system, i dont have an RO system 40ppm water and if i slack for one second i will have a slower cal def and an immediate mag def in days, now as for the dropping nute strength, thats frucking fantastic!!!! its better that it goes down than going up, this shows your plants are taking up nutrients faster than water and are hungry and ready for the next step. that being said, a wise old hippy on here told me this....WHEN IN DOUBT FLUSH IT OUT! flush with plain PH'd water for 24 hours and resume feeding at ec 1.6, and if she drops from there bump up the nute strength and make sure your meters are good and calibrated...i just took a look and read you do not have fresh air? if your not bringing in fresh air you must supplement with co2, plants dont need fresh air, they need the minimum levels of co2 that come in with the air. these are fast growing plants, and with co2, light water and minerals will photosynthesis occur, the plants need these element to create the energy to grow and thrive via the production of carbs, you can hinder this energy production bigtime if one of those elemnts is not abundant, plain and simple