Sizeable job, lots of algae

I have the largest house to date coming up and it is just loaded with algae. I’m new(ish) to downstreaming, did a few searches and can’t quite nail down what mix is needed after the last housewash fiasco. I’ve used my jrod three times so far, going to be interesting getting up to the third story in the back.

Straight undiluted 12.5% seems a bit strong, should I be doing a 1-1 instead?

Oh, and I’ll probably be running about 200’ of hose on this sucker if that makes any difference.

It depends on various factors. What kind of siding? What is the dilution ratio of your DS injector? Generally for vinyl or hardiboard you want a .6-1.2% solution hitting the surface. You’re probably going to need to push it up higher if the algae is bad. Start low and adjust higher.

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Thanks. 10-1 GP injector, vinyl siding, maybe a little brick thrown in although that’ll be handled with the turbo.

I guess 1.2% is the best I can expect without using my M5.

BTW how is that insurance thing going?

Brick you’ll want to hit harder. Around 3% hitting the surface.

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Got a pic?

Unfortunately no, I was so busy giving a bid I forgot to snap a couple. I’ll try to do some before and afters tomorrow.

ALWAYS - Always take pics to protect yourself and so when you ask one of your many questions we’ll know what you’re talking about, lol.


I’d start the job with a test batch of 1 gallon SH and 1/2 gallon water. Then you have plenty of space in your mix bucket to up the strength as needed.

But honestly, as long as you’re careful to water and rinse all surrounding foliage, you could DS straight SH and be ok. Just might be a waste of chems.

If the growth is just sloughing off moments after your mix hits the siding, then you’re on the hotter-than-necessary side. If it’s taking more than a couple minutes for any noticeable change, then you could probably bump up your mix strength.

For really bad houses, plan on doing a few applications of chem; the growth kind of works off in layers. Make sure to allow dwell time between applications, though.


Thank you! I used straight 10/12% and Jrod, just melted that crap right off in 7 minutes. Easy peasy.

I did have to hit one spot twice but no biggie.