Hi and welcome to garden.org. Could you please give us more information before we attempt a guess?
First of all we need to know where you are - you can fill in that info on your personal profile (the little person icon in the blue sidebar at the top) so your city/state/country will appear in your posts. Just a zone doesn't help, since we need to know what the weather has been like in your area recently. Hot, rainy, humid or dry etc.
Second, how deep is that tub they are growing in? Is there good drainage? When you water them thoroughly, does lots of water come out the bottom? What kind of soil did you use in the pot? Is the tub in the sun for most of the day?
Third, is that fertilizer a pelleted, timed release type or do you dissolve it in water to apply it? The leaves don't look like they've been burnt by fertilizer, and the green parts are a pretty healthy color.
Could you also post some more pictures - the whole plant from the side view, a close-up of one of the affected leaves, both top and bottom, and a close-up of the stems too?
