# Downstream ratio

**URL:** <https://pressurewashingresource.com/community/t/downstream-ratio/1888>\
**Category:** Residential\
**Created:** [July 8, 2013, 8:36pm UTC](https://pressurewashingresource.com/community/t/downstream-ratio/1888 "2013-07-08T20:36:57Z")\
**Posts on this page:** 1\
**Showing post:** 2

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**Author:** ![Tim4](https://pressurewashingresource.com/community/user_avatar/pressurewashingresource.com/tim4/32/1431_2.png) [@Tim4](https://pressurewashingresource.com/community/u/Tim4)\
**Post date:** [July 8, 2013, 9:14pm UTC](https://pressurewashingresource.com/community/t/downstream-ratio/1888/2 "2013-07-08T21:14:54Z")

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> [@AdkinsCleaningSoluti](#):
>
> Hey guys, rookie question again, how do I calculate how much sh % is getting on the house. I have a 20 to 1 injector, 4 gpm pw, using 6% bleach. If someone could give me a formula on how to calculate it I would appreciate it. I’m using straight sh right now, no added water. Seems to be working really good just want to make sure it’s not to much . Thanks

You have achieved nirvana when it seems to be working good. As long as it takes a few minutes to begin to see results, you’re not too hot. Ratio numbers, percentages and the like are nice but what happens when you wash in the shade vs. the sun? Do you need a different ratio then? What happens when you get two month old bleach vs. two week old? What happens when the outside temperature drops twenty degrees? All of these things affect your cleaning as well as the effective percentage on the wall.

It’s nice to know numbers, it’s better to know how to wash. And it seems like you are getting there.

Start with a five gallon container full of water hook your down-streamer to it and add the amount of pressure hose that you usually use. Start your pressure washer and spray your gun into a fifty five gallon container. When it has fifty gallons in it, stop. Measure how much has been drawn from your five gallon bucket. Let’s assume three gallons. So you have 47 gallons of pressure wash water and 3 gallons of soap. Let’s call that 47/3. That equals 15.6 to 1. If you are using 6% bleach, divide 6 into 15.6. Answer? .3846. You are getting .38 percent bleach on the wall. Now what? You should get nervous because everybody knows that .38% bleach on the wall will never work. But you just told me that it did.

Holler back.

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