sounds like it yes. you dont have any gypsum in your soil?
when it mixes with water it becomes a basic pH. so having gypsum powder in the soil will buffer the pH if you are watering in an acidic tea or tend to have an acidic soil/compost. you can make a gypsum tea tea also. itll have a pretty basic pH.but this would be guess work if you wanted to bring your pH up this way. ive done it and it worked but i was outdoors and had to water daily so there werent many lasting effects of high pH since the next day and next day etc the gypsum got watered out.
hence the problem.
the subcool method is really an inferior one.
With good organic soil I don't even worry about soil ph only the ph of the water I put in. With super soil to don't do it like when you ran synthetic nutrients you don't want any runoff. Just water until just a little comes from the bottom and let it soak it back up. Also I would water once every seven days with great white or mammoth p I chose the latter as it works really well and does wonders in super soil and regular soil grows. Like grease monkey said don't give up on the organic stuff man it's worth getting it down.
