my roof water is about 7.3 to start with and goes to about 7.6 over about 3 weeks to a month. The LFS said that was too high and sold me some PH down.
I have small coloured gravel in my tank and 2 pieces of terracotta pots. The fish have are 3 swordtails, 2 neons, 1 harlequin 1 Siamese fighting fish, 5 mountain minnows and 2 bristlenose 1 skunk fish.
When my fish die there is no visible sign of diease, one day they are fine and a couple of days later are not in sight! The LFS tested my levels last time and there was no nitrate/nitrate/ammonia showing up.