Hydrochloric/ muriatic acid, distilled or bottled (RO/DI) water mix are also some options. The problem with acid is similar to peat, KH will always be replenished from your source and this will cause some headaches and TDS swings. Mixing with 0TDS water like bottled RO or distilled is simplest and most effective by diluting the source before it goes in the tank. Buying your own RO is a no brainer once you lug bottles home for a few weeks and start adding cost. After that you'll start pondering an auto water change system.
