I'm a bit confused, what type of pests are you trying to irradicate. Is this a foliar spray for mites or thrips or something, or are you using this as a soil drench for gnat larvae or what? The reason I ask is that it is basically counter productive to use any type of pesticide soil drench if you are growing organic as this is going to have a very negetive affect on your mediums biology, possibily killing all of your beneficial bacteria and fungus...
Also if you are growing organic then i would avoid altering the PH much unless it is a necessity, the microbes the thrive in organic situations will buffer your medium as the release enzymes and acids with is also how nutes become available to your plants. I am a 100% organic grower and do not even own PH up or down. The are tricks you will learn along the way of natural items to lower or raise the PH like: Calcium carbonate ( lime and eggshells ) raise PH and have buffering ability for acidic mediums like peat, while most organic nitrogen and sulfur sources will lower the PH. All of these work in conjuction with with microbes to release the nutes and buffer the PH.
So let me know what type of pests your dealing with and we can see if there are any alternatives to the pesticide.