You can't get an accurate runoff ph using aquarium or pool kits, nor the strips. They have a color-coded result based on a clear-water test. The runoff tints skew results. Ok for ingoing water ph, but not for runoff. Soooooo...Doubtful your runoff is really that low. (hopefully, lol)
Most potting soils are pre-buffered, and the buffering seems to last 3-5 months depending on brands.

Some compost mixes have stuff ranging from tree and leaf litter to chopped-up roadkill, so can have vastly different results.

You shouldn't feed them till they've got 4-5 nodes. Then start with 1/2 strength nutes and watch their reaction. Go from there....