high alkalinity

Hi! So I've been trying to lower my ph in my tank from a staggering 8.4. I was wondering if i should use distilled water because I've been doing water changes with my R/O and some "api PH DOWN". It doesn't seem to be working that well I've done about 4 water changes with that method. Perhaps my...

i have two betta males in separate 5.5 gallon tanks. Both tanks tested high for alkalinity and slightly high PH. I know a ph swing can be harmful so how can i lower the alkalinity (and in one case soften the water) without drastically affecting the pH level?