Help! PH or Nute problem

I just started flowering these white widow plants when within a week I noticed brownish white spots forming on the edges of the fan leaves. They worked there way towards the center of the leaf. The leaves look like they are burnt but they are not crisp to touch. The leaves are either curling inward and down or upward like a "U" shape. New growth is also a lighter green color and somewhat pale. The problem has gotten worse in just a short period of time. I am pretty sure i am dealing with a nutrient deficiency, but it could also be a PH problem. I looked at a few websites on nutrient deficiencies and I bought some CAl-MAG to foliar feed with since my plants look like either a MG, Fe, Zn,Mn, or N deficiency. I was hoping someone could clear that up for me. I have always grown in rockwool and kept my PH fairly low. I just decided to try out a coco/ perlite mix and feel maybe my Ph is too low (about 5.7). I am using the same nutes I used last year in the rockwool with the same strain and didn't have this problem.
The only other change I made is that I had to ditch my RO filter from last year and am now using a product from Hydrologic called the small boy. Its supposed to take out the chlorine from the tap water as well as some larger particles but I'm still getting about 460 PPM water compared to the 10 PPM water using the RO filter.
Anyways, here are some pics of the leaves and I hope someone can help me. I just flushed all the plants using Clearex and measured the runoff to about 700 and PH between 6.2 - 6.6. Is there anything else I can do? Are my babies just mad at me for giving them crappier water?

 

I just flushed them and the runoff measured averaged around 6.4. I am using advanced nutes 2 part formula with their carboload, and big bud. I just bought the CAl-MAg and only used it as a foliar spray. I plan on letting the coco dry out for a day or two before I try and correct the problem. I am going to hand water them and foliar feed untill I see some improvement. Since the PH is in the mid 6's should I water them with a PH of mid 5's? I use the Advanced Nutrient's nutrient calculator to figure out the dosage of nutes. Last year, When I was using RO water (PPM of about 10-20) at this stage of flower (10 days) with the Advanced Nutrients, My PPM was about 700. What should it be if my starting water is above 450 PPM? How long should the CAL-MAG take to make a noticeable difference. The temperature at the plant tops is about 84 F. The light is an air cooled 1000 watt HPS and is about 18"-20" above the plants. I will be posting new pics tonite.

 

How do you clean the coco before use? I'm not going to let it dry out, but I don't want to overwater them. Right now since they are still young I water every other day.

Hey chilly, how should I adjust for the hardness in my water? How can I make sure my plants are getting K and Mg if my water is as hard as it is? Also the runoff when I flushed with a few gallons of water was 700 PPM. My rez started at 1108 PPM and within a week it moved up to 1287 PPM. I was adding PH adjusted water to try and stablize it at 1200.
I think I might break down and buy another RO unit. I didn't realize how ineffective the SmallBoy unit was. Besides, I'll save money by not having to buy bottled water.

 

Here are some more pics. Another symptom I noticed was that the stems on some of the larger fan leaves are weak and limp. The leaves don't look like their stretched out and soaking up the light. Some are twisted or turned upside down.