We used to use Captan in our spray program for the grapes but found it's efficacy to be weak.  After doing some digging our spray water pH was too high and apparently Captan has a half life of minutes in spray water above 7.5 pH.  We have a lot of calcium carbonates in our water.  Sure does taste good but no bueno for use of Captan.  We'd like to get Captan back in our program because of cost and supposed efficacy regarding downy mildew.

I have a good pH meter and our water starts at 7.47 pH.  I thought adding the equivalent of 17 lb/100g h20 AMS would be a good start.  It dropped the pH immediately to 6.7 and then came back up to 7.37.  Not a significant drop.  I do have semi bulk citric acid on hand (used as a disinfectant in our other operation here)

I have seen many commercial products but figured someone on here has gone through this exorcise once before.  Looking to get into that 6.0 range

Question: 

Can citric acid be used to safely lower the pH for the short term use?

What is the "best" commercial option that would be simple to use/measure?

Thanks in advance.

~Joe