Spider mites and P.H.?

Currently growing hydroponics indoors. Recently found spider mites four weeks into flowering. Already treated with Neem Oil, seems to be working. There is new growth but the leaves are a light green color, and can't get the P.H. above four.

Is this caused from the spider mites?

Also, recently emptied out three gallons of water and replaced with new water.

How can I get the P.H. up?