Not sure what you mean there. You’ll never have a stronger mix than 12.5%. You might be thinking of batch mixing for roofs and mixing 70% water to 30% SH.
To find out what your draw rate is search for “bucket test” on here. You’ll find mutiple posts explaining how to do it. Racer has a good explanation on here somewhere.
Most use 10% or 12.5%. Whichever is available to them. Say you have some concrete that is covered in algae and you want to use a 5% mix. (Soap, water, and sh). With 10% SH you would need to fill a sprayer or tank with 50% sh and 50% water. That will give you a 5% sh mix. Say you wanted you mix to be 2% sh. You’d then mix 80% water and 20% sh which will give you that 2% mix. You’re basically using percentages to get your mix rate. @qons Mike can probably explain it better. Ratios are probably easier. I just basically go by fractions. Half a pump up of sh is 5%, 1/4 of sh is 2.5%, etc. Just keep it simple. You never have to be exact with your mix. Just close.
@JBsPowerWash to add to what @marinegrunt said just above - that method of making a particular percentage is only accurate when it comes out of the spray tank/bottle/sprayer/pail WITHOUT further dilution.
1/2 of a gallon of 10% bleach and 1/2 of a gallon of water will get you 1 whole gallon of 5% mix.
IF you where to downstream from that container of 5% mix you would be “watering down” or diluting that mix as its being picked up through the siphoning tube (AKA drop stick) and mixing with the water coming through your pressure washer hose. Your particular downstream injector, length of hoses, etc will determine how much dilution is happening.
But, as many have said before, you don’t have to be precise on your ratios - just remember that if the mildew/algae turns brown or completely disappears your mix is working. You can fine tune it to work faster or slower with more bleach or less bleach.
This is a SH Mix Ratio Calculator I made to make it easy to
calculate the strength and weight of your Batch Tank.
Input into Calculator:
Total Batch gallons needed
Starting SH % strength
Final SH % strength needed
Open file with Google Sheets, or MS Excel.
Edit values in green cells only, all others cells should be protected from edits SH Batch Mix Calculator Download Link