Since I am just staring my company, I have not yet invested in a surflo and water tank yet, but it is on my to do list. I used a 50/50 Sodium Hydroclorine 12.5%/Water and added a little TSP. I sprayed the roof with a pump sprayer and hit it with my soap tip. This caused it to suds up pretty good. I let it set for about 15 minutes and then came back and hit each tile one by one using only the soap tip (minumun pressure) that took the black off pretty good. Should the bleach/water simply disolved the black streaks?
When you sprayed the mix with your rinse tip, you may have diluted it!
It needs time to work.
Pump sprayers are not generally uniform in their application, and often can not get enough on to do the job.
TSP in weak solutions is not to be feared, and will only help clean a roof.
The Cleaners of the past used TSP all the time to clean houses with, along with bleach.
If used at 1/2 cup per gallon of mix, or less, there shouldn't be any problems.
But, if a little is good, more is better, right ?
Nope, more can cause problems.
The only time we go to 1 cup per gallons is on a filthy white tile roof, and we have ground man watching out for run off, and promptly dealing with it.
IMHO, you need to consider getting a chemical pump.
I suggest a Delevan, they are under 150 dollars.
One roof will pay for it!