For some reason, I tested my water the color like almost dark blue (API test) for PH I think it's more than 7.6 ppm in my Red Fire shrimp tank (3gallons). Do you think if I take out about 1.5gallons, add in RO water (without minerals) would low PH down?
7.6 isn't bad for them and they'll have no problems. But in general pH < 7 is what most consider ideal for shrimps. If you want to lower the pH naturally then add indian almond leaves since this also contains other tannins that are beneficial for the shrimps.