I have an Eclipse tall 37g tank with the in-built filter system. Tap water pH is 7.8. Would like to drop it to a neutral pH level. Have tried adding acid drops/acid buffer. And even though new water pH is way low (6.0), pH spikes back to 7.8 in the aquarium with a day even with 30% water change. Any recommendations on how to lower the pH safely and stabilize it at that level? Please be specific with product names. The ones that I tried did not work. Thanks.