Lowes, Home Depot, Walmart, all those don't carry squat for hydroponics nutrients, and the soil-based stuff they have is of dubious value.
Garbage in, garbage out.
Give your plants a proper, balanced diet of some quality nutrients and they'll thank you for it by growing big and strong.
Don't forget that plants have immune systems too - the healthier they are the better they resist all the many problems that plague growers.