stable water conditions

I have a 10gl freshwater aquarium. I use my tap water and treat it with "nutrafin tap water conditioner for bettas) and a filter. I have; 1 betta 1 molly 4 tetras I did a tip test and my GH and KH are both at the max (180 and 240) my PH is 7.5/8!!! I've been cycling the water and treating...

I am setting up a black water biotope 50 gal aquarium, and a similar 35 litre quarantine or hospital tank. I ran the 35 litre tank with sand, bogwood, and almond leaves and the ph stabilised at 6.5, with GH at 3o DH. I then added Nutrafin Aqua+ to remove any chloramines, chlorine or heavy...