first off, pH right out of the tap is not your "actual pH". You need to let it sit out for 24 hours, and have an airstone running on it first. My tap water is 8.5 out of the tap, with a KH of 36ppm. I wait 24 hours and it drops to 7.3 pH.
You say your tap water is soft out of your tap. What is the basis for this? i.e. what is your KH out of the tap?
@ 300ppm KH, your pH should be at ~8.2.
What substrate do you have, what rocks do you have, etc?
Post the answer to your tap KH and the above and further analysis can be done.
450g Planted Discus Tank - Work in Process!