Don't resort to using any chemicals to adjust your pH. They are dangerous to the health of your fish and are basically marketed so that the companies can make a lot of money on folks that don't know better. These chemicals will end up causing wild swings in your pH that can kill your fish, not to mention drain your pocketbook. Remember, more than any specific value, you are looking for stability. There are better ways, already suggested previously, that will work for the long run and are not just a band aid fix. And 0.50 ammonia in your tap water, cut to 0.25 after 50/50 mix with RO, is not an issue. Your bacteria will be able to chew through that over night. And as MummaOfTwo said, Prime is fine with snails.