I just finished fighting this same battle. Using B'Cuzz coco w/added perlite. Nutes are H&G cocos A+B with Roots Acc. and some others.
What i found is that H&G's feeding chart is way too aggressive for most mj plants, especially ones as small as those. I would ignore their suggested amounts and just follow the regimen as far as when to use which product based on the age of your plants. I base my amounts on the PPM of my water. If you don't have a Ph/PPM meter then you will not have success growing in coco. During veg, you should keep your plants around 400-600ppm, depending on strain and lighting conditions. During the later stages of flower you can up it to 1000-1200, maybe more, a lot depends on the strain.
I would half the amount of roots acc you are using as well. That stuff is potent and I think about .5ml/gal is adequate. Also keep in mind that you will need to pick up a calcium and magnesium supplement as coco tends to hog both. I use Cal-Mag Plus from Botanicare - it also has some iron which is helpful. I wouldn't add the Cal-Mag right away, but keep your eyes our for signs of Calcium or Magnesium deficiencies and treat as needed. I tend to throw a little in every watering during flowering.
Also, get some kind of enzyme to add to your nutrients. These enzymes help break down the salts that can build up, cleaning your medium and helping roots to absorb more nutrients. I like Hygrozyme a lot, but recently switched to H&G's Multi Zen - their equivalent product. I like Multi Zen because you use a lot less per gallon, but I think I might like Hygrozyme a little better. Either will help you.
Make sure when you water that you are watering in the 5.6-5.8 Ph range. 5.8 is what your are really aiming for, but I find that as salts build up the Ph of coco can rise easily. Also, some nutrients like phosphorus and potassium are better absorbed below 5.8 so i often water at 5.6 to balance it out a little.
Also make sure that when you water, you get at least 10% runoff each watering. Salts build up easily in coco and the number one way to increase salinity to harmful levels is to water without runoff.
Your plants look like they are suffering from a combination of high Ph and nutrient burn, as well as nutrient lockout from the high Ph. You will want to slowly adjust this over the next week. Do so by pouring copious amounts of Ph adjusted water through your containers. Start with some 5.8 Ph adjusted water and measure its PPM's so you know what is going in. Water slowly...this is very important. If you water too fast the water doesn't have time to sit in the soil and absorb the nasty salts your are trying to remove. Better to water each plant a little at a time, and move through the garden that way each plant has a good gap between wettings.
Once you see some runoff, test it with your Ph/PPM meter and see the difference. Fore example, when I first did this to mine I was having the Ph go in at 5.8 and come out at 6.6, the PPM in at 185, out at 1800. That showed me that I had a large build up of nutrient salts, the 1800 ppm, which was causing my high Ph. Salts are basic and therefore raise Ph. The more salts in your soil, the higher your Ph.
Once you have determined you have a high Ph, you can flush it with some lower Ph water to help get it back in line. I wouldn't go much below 5.2 though or you risk burning your roots. If only your PPM is high, but not your Ph, then you would want to flush with 5.8 Ph clear water. Again, go slow adjusting the Ph. It is better to slowly adjust it Ph down over a week or more than to flush 30 gallons through in one night with super acidic water. You will stress your plants if the Ph swings too much too quickly.
Also, check your tap water. If your PPM is much above 300 will want to invest in a filter or buy filtered water. Reverse osmosis is good, but expensive and comes with some other concerns. I use a Small Boy filter and it works great. Doesn't lower ppm much but it does remove some contaminants. The plants love it.
In the mean time, you can foliar feed to help your plants get nutrients that are being locked out of the roots. This can really help the problem from getting too much worse. In the future I recommend going much lighter on nutes. I would rather fix a deficiency than a toxicity any day, way less work and way less stress on the plant.
