By 'automotive' I'm assuming you mean automatic? If not, please let us know what you mean. That description sounds a bit like like an autopot system. How big is your reservoir? What's your grow medium? the 5.8 PH would be OK for coco. What are you using? Have you tested the PH of your water before adding your nutes? You should know that number. For me, tap water is 7.1. I'm adjusting the PH downward most of the time. Do you have to add PH up or down to get the PH to 5.8? BTW, what are you using to adjust the PH?
What does the 1.8 signify? Is that the EC of your nutrient solution? What brand/kind of nutrients are you using? Is your reservoir aerated? Using a small pump timed to run a few minutes a few times a day will def help stabilize the PH. I wouldn't use an air stone. I ended up buying a PH controller to stabilize the PH. When are you measuring the PH of your nutrient solution? Have you added all of your nutrients to the water before you test? Gives us some details.