Controling PH

[Fantast Bronson]

I'm a bit concerned about my pH levels(6,6). The fish I've got are fine with this level but my concern is that if my No2 levels should rise suddentley my pH is so low that there is a chance for Nitrous Acid to occur.
I have tryed to buff the water with Proper pH 7.0 but it doesn't seem to work, and I dont think it is a good idea to use chemicals in the tank? Any ideas??

 

[dan dan the fish man]

have u tested the water that u do the water change with ?

 

[Fantast Bronson]

have u tested the water that u do the water change with ?

My tap water is about 6,6 as well.