[Delphinus]

You'd really have to overdo it, IMO, to worry about crashing your tank.

For the most part, pick a pH you're comfortable with. 7.5 is OK, but you can safely go a bit lower. I target mine at 6.7. Whatever the flow rate, bubble rate, etc., just know that you want the pH to be at your target.

Depends on your tank size of course but basically start with a slow stream, say, 60 ml/min, and whatever bubble rate that gets you that target pH.

Let it run for a couple of days, then test your alkalinity and calcium. For the most part you need only test Alk, IMO. Both Ca and Alk will be added together in a fairly balanced manner (exceptions may apply but let's not worry about it for now).

If your Alk is where you want it, great, you're dialed in. Test again in another couple days to be sure.

If your Alk is lower than where you want it, dial up the reactor. Both effluent rate and bubble rate. If you started at 60 ml/min, make it 75 ml/min. Or something, you get the idea. Adjust the bubble rate again to get pH to target. Test again in a few days, etc.

If your Alk is higher than where you want it, then you can dial down the reactor.

It will take quite a few days of fiddling with the flowrates and bubble rates, but I find if you just stick to a target pH and adjust around that, then at least it's a little easier.