Low Run-Off pH. Soil Additives to Raise pH

So I've had real low run-off pH almost my whole grow. I was using Happy Frog soil and my run-off would always be under 6. The low pH of the soil caused an Mg lock-out, which I fixed but not easily. I've tried everything to raise the pH but have had very little sucess.

The next group of plants I potted I used this: They're still babies but the run-off pH is still like 5.9. So I fear I am going to have to fight this same battle trying to raise the pH of my medium.

On my next grow I plan on using the Pro-Mix again, but I was thinking of adding something to raise the pH of the soil. I know dolomite lime works, but I don't know how much to add. I also don't know if there is something better that works. I saw a bag of some soil additive that was made to raise pH (They had one to lower pH as well), but I just glanced at it don't know what's in it. So what should I use to raise the pH of my medium and roughly how much?

Thanks in advance RIU.

What are you measuring the run off with?

Powdered dolomite lime.

Around here, Lowes is the only place with the powdered. On the bag it's marked 'ground dolomite lime'. Every place else just has the pelletized, which just takes too long to work (2 months+).

"I" use 2tbl/gallon of mix or, 1cup/cf of mix. Add to the mix BEFORE use/planting.

That 3.8cf bale will expand to ~7cf, so add accordingly.

Wet