i got sort of lazy and didnt read everything.. so i might be spitting back some repeated information... but here's what i think...
i think you have a ph problem... mostly with the soil... soil ph and water ph do not have anything to do with one another...
to begin with make sure everytime you water you are adjust the ph of the nute solution after you add nutes... adding nutes to water will lower the ph... so depending on the beginning ph you may need to adjust it.. but you should check it and make sure its with range everytime for good habit...
if you need to lower it you can use lemon juice.. to raise it you can use baking soda... amounts will vary.. so add a little, check, add a little, check.. better to be safe than have to re adjust in the opposite direction...
if your soil ph is incorrect it can set off a chain of events that can really fuck things up...
salt build up from nutrients in the soil will cause the ph to lower.... if as the ph lowers, different nutes become less available... as those nutes become less available, they begin to cause more build up.. the more build up the more the ph lowers... the more it lowers the more nutes become unavailable.. ect ect...
having a ph soil test kit to check the ph can save a lot of time trying to figure out plant problems... if your ph is correct then its a lot easier to know its a deficiency, and which one... trying to fix a deficiency with a ph problem will only compound the problem more... if you havent already, you may want to purchase a soil ph test kit and check the actual soil ph....
i have read about the water issue, so i wont go to much into that... but using RO water is going to be safer than anything.. a high ppm water can cause build up in the soil and start affecting ph as well...
using hydrated lime will raise your soils ph... hydrated lime itself is ph'd at 7.0.. so if you do use it your soil will eventually even out at or close to 7.0.. this is acceptable for your soils ph.. and, with the use of nutes, the soil should actually be slightly under 7.0 which would be perfect..
if you need to lower the ph using sulfur, magnesium sulfate, or gypsum work.. you may also use a soil acidifier like this
http://www.planetnatural.com/site/chelated-iron.html
again, its better to use a little an adjust over time then try to adjust all at once.. follow the directions on the product to get to your desired PH... and try to adjust no more than .5 at a time.. to much of a swing can cause osmotic shock, which affects the roots..
obviously i suspect you have a nute deficiency.. but it could be a ph related issue.. if you are feeding with good nutes, and are using calmag, or if you are using a 2 or 3 part system, your plant should be getting everything it needs, which helps point even more to the ph issue.. but you cant tell until you get a soil ph test done..
one way to avoid ph issues is to adopt an "every other" feeding schedule where you feed with plain ph'd water one time, the ph'd nute water the next, then plain ph'd water, ph'd nute water, ect. ect...
as i said water ph and soil ph dont relate much at all.. but making sure the nute water you are feeding, and keeping all the nutes available when you feed, can help reduce the amount of build up left behind, which can help maintain soil ph...
if you havent flushed you may want to... it cant hurt... flush with a 1/4 strength nute solution.. that will actually remove more build up than plain water will.. try to get a soil ph test kit and see where the soils at...
if you have done one or more of these things please let me know and ill try to help from there...
sampson