I try to advise against using carbon based sources for raising or lowering pH. In small amounts baking soda and acetic acid are fine. But I would never recommend using carbon based additives for pH on a large scale in reservoirs. Carbon creates solids and sludge.

Every water source on earth has a little chloride. Don’t go thinking you need to remove it or that it kills microbes. Chloride is an essential element required by plants. Your plants would die without it.

You can let it sit for a day without an air stone to allow chlorine to evaporate from your city water. Air stone will speed up process. If your city water has chloramines in it, then you’ll need an activated carbon filter to remove them.

Citric acid can be used to lower pH but as you’ve found out it’s not stable. Phosphoric acid (H3PO4) is a more useful acid found in most pH down products as it also becomes plant food as it breaks down.