I'm guessing the reason pH is decreasing is the chlorine that is coming out of the water. Try using an air bubbler on another sample and see if the pH changes. Looks like your water is very hard and that is not necessarily bad for your plants. You may need to take that into account if you are fine tuning your nutrient solution. Try dropping the pH by using an acid like lemon juice and see if the cloudiness goes away.

It COULD be high calcium hardness level, high conditioner level, high pH, high total alkalinity, high level of total dissolved solids, low chlorine level, algae, large volume of microscopic particles in the pool water, or filter/ filtration problems.
Or it COULD be that your area (*like mine) has switched to chloramine ;) Check with your local water provider as chloramine does not gass off in 48 hrs liek chlorine..it takes weeks (*and clouds water at high levels)