Hi and welcome!

Some pesticides are very powerful and almost always leave residues, be it on the plat or in the soil. However, that doesn't mean you can't use the plants or the soil anymore. Pesticides was over time after you stop using them. Of course, it'll take more time for them to go away if you've been using them for long.

During that time, you can still use the herbs, but be sure to wash them thoroughly (you can use a mix of vinegar and water or one with lemon, water and baking soda).

As for changing the plants to new pots, you should certainly consider that option. A healthy environment and a rich natural soil will make a huge difference in your plants. In fact, having that healthy environment will also help against plagues, since it'll make difficult for them to reproduce.

Finally, you should plant some yarrow, which attracts predator insects (ladybugs, lavewings) that will eat harmful insects and their larvae. You mentioned you had a problem with ants. Next time, use vinegar and coffee grounds in the soil, instead. They will surely drive away the ants and protect your garden.

Hope this helps!

Learn as you go. You can't do everything the organic way the first time out, but as you learn about more things like organic fertilizer or pesticides, then incorporate those into your balcony garden. There will come a time when, from start to finish, you did everything as organically safe as you could.

Of course you can go organic!

Just stop using that chemical stuff & use organic methods instead;

in this day & age of gardenweb & google, you can find organic remedies & methods for everything.

If the budget runs to it, I my own self would dump the old soil, wash the pots in vinegar & dish soap in hot water, & use new, uncontaminated soil.

Best luck, & have fun!

In addition Diatemacous Earth works very well on ants. You can get food grade very cheap so safe for pets and humans.

You can buy small bags of Neptune's Harvest potting soil, or at any nursery you can buy local finished compost. I would stay away from chemicals, and definitely away from Miracle Grow