minimum pot size should be 1 gallon per foot of plant you want to grow or 1 gallon per month you intend to keep the plants alive. when you flush, did you check the runoff PH? what many people dont notice is that salts build up in your medium and you can be feeding 6.5 water and it can come out 7.5, thus locking out your nutes, when i see issues like yours, ya know discoloration and necrotic spots at the TOP of the plant, its either a hard to get micro element or PH/Rootzone issues. looks like P and K defs rolled into one, but you need to check the PH of water as it comes out of the bottom, also when flushing, say your flush is a 6.5 water, keep flushing and checking the runoff till it gets close. all it takes is a months worth of feeding the plant to get significant salt build up, and these buildups/lockouts and puzzle most new growers
