You just dont need the canister (can cause problems down the road , high nitrates), The live rock and the
protein skimmer is all you need. I dont use a Protein Skimmer, I have a bit of a different setup. But most folks do and I'm sure one of the will give some recommendations.
PH problem??? Have you tested the PH of your fresh Salt water before it does into the tank? Are you using RO? Do you have good water movement in the tank? Lets hope one of the expert salty dogs is reading this and will sound in. How often are you doing water changes, how much are you changing? How deep is your sand bed?