Maybe next time you could mix a little lime in with the soil before you plant in it.

I figure you're probably using some kind of peat in there?

Try a flush, then balance the feeding solution ahead of watering.

If you don't want to use pH down, and you're in the know of how much your pH is off, you sould use those Sodium Hydroxide pellets for cleaning the drain, be careful for yourself, and your plants! But it works.