over feeding your plants will cause a nute buildup, and that will cause the ph to go down, think of it like this.....ph goes up they need more nutes, ph goes down means too much and they need a good flush.
IMO this may be from reusing your coco and not properly flushing the coco between runs, causing a salt/nute buildup
IMO this may be from reusing your coco and not properly flushing the coco between runs, causing a salt/nute buildup