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The pH should come down over time. How long this takes depends on the buffering of your water and top up water. It's usually not to long for this to happen.
You can also adjust it down slowly by adjusting the pH of the top up water before you add it to your system.
Observe all precautions for using Hydrochloric acid (HCl)(aka muriatic acid) - Add to topup water, not directly to system water - adjust top up water to 6.0 to 6.5 and let stand several hours. Check the pH before adding to system and adjust back into range if needed (if you have to adjust then let it sit a couple more hours).
By adding a bit at a time like this, it will lower the system pH gradually. Try not to change the pH more than 0.4 pH points since more rapid changes can cause problems for the fish.