There are a few ways that we can change the pH of water:
A calcium carbonate filter: Theoretically this brings the pH to neutral. However, I've found that it takes a full 10"x2" cartridge to achieve this. The smaller "in-line cartridges" are not very effective.
A magnesium carbonate filter (sometimes branded as Corosex): This will bring the pH up to more alkaline levels. However, it is not consistent and results in initial very high pH spikes and then settles to influent pH level very quickly
A Biocera filter which is a combination of calcium, magnesium, sodium, potassium and tourmaline: Of all the methodologies we have found this to offer the most consistent alkaline pH - usually between 8 & 8.5. This filter has the added benefits of lowering the Oxidation Reduction Potential (ORP). This is thought to give the water antioxidant properties due to the release of molecular hydrogen.The tourmaline is thought to reduce the size of the water molecule clusters and to make it easier for the body to absorb. It also emits far infrared rays which are thought to have healing properties.