Firstly, nutrient "lock out" is caused by either extreme acidity or extreme alkalinity and is a soil condition, not a nutrient problem. To many growers surprise, no doubt, nutrients only become "locked up" with acid conditions of about 4.0 and lower, or alkaline conditions of about 10.0 and up! The often quoted figure of 6.5 is about just right, but nutrient availability is almost 100% anywhere between 5.5 and 7.5 so being anal about pH is not really as critical as some people would make you believe; just google "nutrient availability and pH".
Your plants to me look like they are suffering more from nutrient over load rather than anything else. I would suggest giving them just plain water until (new) growth resumes normally, then progress to feeding the quarter strength nutrients every second or third watering. The substrate needs to be moist all the way through after watering, not soggy wet or with dry patches either. This is a careful balance to maintain, but will get easier with experience. Then let the substrate dry out a while, until the top inch and a half or so is dry, before watering again. This could be anywhere between 1 and 7 days depending on temps, water requirements of your individual plants, container size, plant size, air circulation, substrate porosity, relative humidity, day length etc. You should try to make sure each time you water that there is water coming out of the bottom of the pots, otherwise there is no way of telling if water has penetrated the entire depth of the pot, this also helps prevent nutrient "salts" building up in your substrate. If your substrate is particularly dry, either from under watering or long gaps between watering, your substrate may have become "hydro phobic", meaning rather than wetting the substrate, water will just run straight through the pot with very little being absorbed. In this situation, it can help to give (for example) 2-3 litres per pot, but spread out over a couple of hours, giving 500ml every half hour x four/six times. This way some water will be absorbed before the next dose of water is given. This also allows the substrate to "swell" a little each time, therefore (eventually) preventing the water from just running straight through the pot without being absorbed. Deep watering to run off is what you should aim for rather than giving small amounts of water often. The roots on your plant will be all the way to the bottom of the pots, so unless there is run off, the roots at the bottom of the pot will remain dry, preventing root growth and hindering nutrient availability. Remember too, nutrients are water soluble, so unless the substrate is evenly moist, nutrients will be unavailable for your plants. Have a look at my diary "Holy Mackerel" / Cannabis Conundrums to see the exposed root system of a 3 week old seedling and this may give you an idea as to why deep watering is essential.
So, after all this waffle - give your plants plain water until they pick up growing again, then start with quarter strength nutrients every second or third watering, until they have been happily growing for 2-3 weeks, before upgrading to half strength nutrients every second or third watering. Giving a dose of plain water between feedings will allow the plant to "scavenge" any remaining nutrients in the substrate, as well as helping to prevent nutrient salt build up in the substrate too. Hope this helps and happy growing!! ,.... Organoman.
P.S. - I also would recommend giving your plants a light watering with plain water half an hour or so before feeding them with nutrients. This way your plant is fully hydrated before having to "deal with" the nutrients. This also helps with nutrient assimilation, as moist roots are better able to deal with any human made nutrients without the roots burning or suffering any other problems, if they are already pre-moistened.
+1 strain
