The answer is yes and no. It depends.
1. If you add evaporation water from the tap it might be increasing your KH and GH each time. The minerals do not evaporate with the water. Plus your tap water isn't good to use. It might be the main issue.
2. If you have any sea shells or coral in your tank it will keep making the water hard and increasing the pH.
3. The substrate has to be inert. Use Fluorite. The Eco soil might cause issues. You can test your gravel/substrate by rinsing some in RO water. Then place it in a cup with fresh RO water. If the pH or KH raise it is a problem. I have fought substrate before that kept raising the KH. The KH would never go lower even using RO water.
4. The rocks might also be an issue. Your decorations could be fighting against you. The rocks must also be inert. You can test like the gravel. Just place in a bucket of RO water.
Until the issue is removed you will add adjusters and the pH/KH might go lower then rebound and kill things. Insure all the items in the tank are safe and not raising the ph or KH. This ACID BUFFER will be great once the reason your water is hard is removed. Use RO water with some electrolyte replenisher. You can also buy a pH buffer that will set the pH at 6.5 or 7.0 Do water changes with lower KH and Ph. Only a little at a time, to slowly bring down the hardness. You might even wait to use pH buffers until you lower the hardness. Be careful with distilled water. It might contain Copper! If the distiller had copper coils!! If you do not have an RO unit look for water that is Micron, Carbon and RO filtered. This should be safe.