That's a tough one. I'd stop with the seachem neutral powder. If you want to try to keep the pH from dropping so low, then try a little sodium bicarbonate (baking powder). Probably a bit cheaper, particularly if you look for it in bulk. You may find it at food supply that sells stuff in bulk. Pool supply would be another option.
As you seem to know, the driftwood is eating up the buffers (alkalinity) and making the water acidic and dropping pH. Adding sodium bicarbonate will replace buffers. It may still be a tricky thing though, to find the right amount to add at the right intervals, so you don't overdo it. A stable pH is better than aiming for a target. The sodium bicarb may raise it higher than 7.0, even to 8.0, but it should also stabilize it. Right now you're on a roller coaster ride. So, I think I'd use the sodium bicarb (baking powder) and experiment with that a bit to find a value it'll stabilize at even if it's a bit over 7.0.
The only other thing I can think of is to get a big backyard kettle and boil the heck out of the driftwood to release the acidifies. You may find that things settle and stabilize once that happens and then the water changes alone can keep it in line. I think I'd do both actually. Boil the driftwood and then add a little bit of sodium bicarb to buffer only as long as needed. In time the acidifying effect of the driftwood should lessen. You could even experiment with this in a big tub, just to get it worked out before subjecting the inhabitants to the changes.
There's a risk in letting pH get too low. See this article on old tank syndrome. Not that you have that, but it tells of what happens when pH is allowed to get and stay too low for too long.
I know I've rambled, but just throwing some thoughts at you.
As you seem to know, the driftwood is eating up the buffers (alkalinity) and making the water acidic and dropping pH. Adding sodium bicarbonate will replace buffers. It may still be a tricky thing though, to find the right amount to add at the right intervals, so you don't overdo it. A stable pH is better than aiming for a target. The sodium bicarb may raise it higher than 7.0, even to 8.0, but it should also stabilize it. Right now you're on a roller coaster ride. So, I think I'd use the sodium bicarb (baking powder) and experiment with that a bit to find a value it'll stabilize at even if it's a bit over 7.0.
The only other thing I can think of is to get a big backyard kettle and boil the heck out of the driftwood to release the acidifies. You may find that things settle and stabilize once that happens and then the water changes alone can keep it in line. I think I'd do both actually. Boil the driftwood and then add a little bit of sodium bicarb to buffer only as long as needed. In time the acidifying effect of the driftwood should lessen. You could even experiment with this in a big tub, just to get it worked out before subjecting the inhabitants to the changes.
There's a risk in letting pH get too low. See this article on old tank syndrome. Not that you have that, but it tells of what happens when pH is allowed to get and stay too low for too long.
I know I've rambled, but just throwing some thoughts at you.
