millstream
Thought I would elaborate on a couple points. First is, that larger volumes of water fluctuate slower. I call it buffer water. Not that the water itself buffers anything, but the larger the volume of water is, the slower the fluctuations take place as the plants take up water and
nutrients. Thus buffering against the natural fluctuations through volume. That's the main reason I always try and use at least twice the minimum recommended volume of water for the plants grown. Not such an problem while the plants are small, but it makes a big difference as they get bigger.
Second thought is I'm not sure how stable the sulfuric acid is. You may try going back to using the normal hydroponic pH adjusters, and seeing if that has any effect. I use the dry adjusters because they are much cheaper than the liquid ones (which is mostly just water anyway).