You need to look into a water filter or R/O filter. 388 is extreme. Do you know what your drinking ?

I like the setup, some day I'll get one.

To find your problem do a test. put one seedling or plant by itself and give it PH'ed tap water. Wait to see if it burns up.

My tap runs about 260 give or take. It takes this water 3 days to turn all the large leaves yellow on a 3 foot bush.

Some places care about what they drink.
Well water at even high ppm's can be great stuff. it's just a crap shoot.

Round here they put wierd stuff in the water to keep the Marines from killing the whole town when they come back and decompress.