The water hardness must be increased substantially, and pH will naturally rise with that. These fish come from Lake Tanganyika, which has some of the hardest freshwater on the planet, and a pH around 9 to match.
The easiest and best way to achieve this is with dolomite either in the filter or the substrate. A substrate of crushed coral sand would be ideal to help in this and be natural. Limestone rocks will also help, but tend to dissolve very slowly. Crushed dolomite is better and more reliable. I've used it with water even softer than what you have for a tank of rift lake fish.
If you go with the coral substrate, adding some Magnesium sulfate [pure Epsom Salt] will add the magnesium and balance everything out. It takes very little added each week after a water change.
You can read more about hardness in this article I posted last week: