Just scrub with soap and water to clean. Then if you want to sanitize, use a spray bottle with about 1/3 parts bleach and 2/3 parts water and spray it down thoroughly, then let sit for about 30 min. But if it is a microbial buildup rather than algae or element buildup, you will want to use new plants and growing media after you cleaned it up. Otherwise the old contaminated plants and growing media will reintroduce the same microbes into the system after you cleaned it out.
P.S.
Regardless if pH issue is a tap water problem or not, I would suggest to use a good filtered water anyway. Unless your tap water is from a mountain stream rather than the typical reclaimed water. It likely has an abundance of chemicals and elements in it that will affect your
nutrient solution balance.