Tell me what happened

Alright, im a nube grower and all, and i have this little problem. I dont think it's serious, but i need opinions. I have one plant, about 11 inches after one month. My first set of one came in great, my first set of three came in great. then my next, it layed before me a 3 peddle leaf, and a four. Its been like this since they've grown. And now what should be my first set of seven, looks like its gonna be a five and a six. Whats F%&ked up?

sometimes that happens from salt buildup or lack of nutrients. pick up a cheap bottle of 7drop Shultz plant food. The NPK is 10-15-10, it's what I use. Started out half dosage then when my plant was thicker I upped it to the full recommended solution.