Oh, you're doing flood and drain.
Is the main part of the medium rockwool or hydroton- are you groing in RW slab or in RW plugs that have been inserted into a bed of hydroton?
In slab, I'd recommend a drip rather than flood.
In a HT bed, I'm thinking here. Hm. Whatever else, you will need to clean out your system- Run plain pH'd water through it for a couple flood cycles and see how much the ppm of the res rises jsut from residual crap that was clinging to your HT. Then dump and re-fill the res with your regular ferts at a lower ppm; try 800 since it's apparent that over 1000 was too high for the plants. And you might try bumping up the pH to 5.8 or so- subtle, but if your meter is even a tiny bit off, saying 5.6 when it's actually 5.4, that would at least put you in range.
Another thing that I'm thinking is, what's the plant mass being fed by that 13 gallon res? If the res is too small, and your feeding is even a little too heavy, again you get a problem with residuals. Think of it this way: You have a bucket of marbles, black and white, mixed up about 50/50 b/w (vague metaphor for your nute solution- bear with me!). The plants use the black ones faster than the white ones. Every time your res level or ppm gets low and needs topping off, you add another dump from the original mixed bucket of marbles. But there were already some white ones in there contributing to the high ppm, the ones the plants don't use so fast. So now your new mix is over 50% white marbles, and under 50% black ones, even if the actual # of total marbles in the res is constant (=ppm remains the same).
Ehhh.... that's such a terrible explanation but the meaning is, dump your res regularly, because unless the plants are using up ALL components of the fertilizer at exactly the same rate, its composition changes over time.
Edit: I totally forgot to say, I think a 13 gallon res may be a bit small for the setup, or that you should do a COMPLETE water change in it more often.
stinkyattic Reviewed by stinkyattic on . Its Always Something... I think this is a phosphorus deficiency, but I am not totally sure. The edges are crispy and the new small leaves around the buds have yellow, crispy, turned down tips. The guide I read said a little P deficiency in flower is normal, but if P is what it is, I think I have more than a little. What should I do? PPM is 1150, pH is 5.6, double checked with liquid pH kit. They are starting Week 4 tomorrow. The last pic is what I would say is the worst looking one. Rating: 5