Coffee grounds are a good soil conditioner, as is vermiculite, but they do both absorb water. The nice thing is when they dry, they shrink, and allow air into the soil as well. Same with the cellulose fibers in compost of any sort. But coffee grounds do not have any nutritive value to speak of. If your weather's been pretty warm, even a slow release fertilizer might be used up by now. If you continue to see yellow leaves and slow growth, you should put down more fert, I think. Even the good quality slow release fertilizers do release faster in warm, wet conditions. So if it says "lasts up to 3 months" I'd bet 2 months max and it will be gone.
Epsom salts is magnesium sulphate, and magnesium is a necessary micronutrient for chlorophyll production (greening) and photosynthesis. But it doesn't have any nitrogen so you do need to add a complete fertilizer of some sort. Veggies are hard working, hungry plants.
