The two smaller plants are getting way too much light, so i'm going to guess this is actually light-related and not necessarily nute-related.
Also, the one plant looks more yellow on the side that is twoard center of tent vs side near wall. More evidence to support the light being the cause if it is not a trick of photography.
Regardless, i can see that the two smalelr plants have nodes that are way too tight and that happens due to too much light. They are also extra pale, anotehr sign of too much.
flushing probably just slowed them down more. no biggie, live and learn.
Get the light right, and that plant will perk up. I'd do that first before adjusting any nutrient concentration, unless it takes a nosedive. Better to do this 1 step at a time. Fixing the light situation may fix everything.