I have found that I really don't need more than that. Perhaps more would better for other people, but if I use too much, my clothes look older, faster, and feel like there's leftover residue.

Both my current and previous washer are high efficiency double load washers. I use 2 tablespoons per wash (1 tablespoon per load technically). It might require more in less efficient machines which do not reuse water in the wash cycle. Hard water makes a difference, also.

The borax acts as a detergent booster but also is used as a bleach alternative. Perhaps adding extra of that to whites would brighten them. The super washing soda also gives the bar laundry soap more umph. Baking soda is antifungal and antibacterial. Part of what makes clothes dirty are those bacteria and fungi. I have washed mildewy clothes with this mix with no residual smell or trace of it.

What you could do is scale this recipe down for one or two loads, writing down your recipe ratios, to fine tune the exact amount that works for your machine and water. Then make the huge batch.

I'm also on septic so experimented Bec I don't want so much draining from the washer into septic tank that it affects that. The septic tank needs the bacteria to break down, and so does the lagoon the septic overflows into, to effectively treat the water.

My motto, less is best. But it'll be different for each situation I suspect. My last residence it took double the amount for same results. The oxy adds extra umph, too, altho tbh I'm not entirely sure how. But maybe that's why I don't need as much.