For washing powder

Add citric acid @ 3%
750 x 3% = CITRIC ACID 22.5g
add extra lye 22.5 x 0.6 = 13.5g
total lye = 13.5 + 137.38 = TOTAL LYE 150.88g
CAUTION: WEAR MASK WHEN GRATING AND PROCESSING SOLID SOAP (it creates a lot of dust from un cured soap & soda crystals when removing processor lid and WILL affect your chest)
cut it into small cubes and grate it when it feels like cheddar. may still be warm. Can use a processor to grate as long as it’s not too hard.
spread grated soap on trays and leave a few days to dry.
Use processor with metal blade and pulverise grated soap to as near powder as possible. If it goes to clumps just leave it longer. Let it dry out and blitz again. (spread out on trays to aid drying.)
mix equal welights of grated dried blitzed soap with soda crystals/washing soda. Blitz in processor. Repeat until it’s powder form. ideally no bigger than ground black pepper.
Store in an airtight tub When dry.
Use a couple of tablespoons of finished powder per load.
If washing in cold water, dissolve laundry powder in warm/hot water prior to use and add to machine as a liquid