I'm using RO/DI in my tank now. my tap water was 8.6 and settled to 8.4 in the tank. The RO/DI water tested at 8.4 but I was told by a LFS employee that RO water doesn't hold pH and that it will crash in my tank. Is this true? And if it is does salt mix (I'm using Kent's) buffer the pH in the water or do I have to start buying buffer now also? This employee says that he goes through a container of Seachem buffer a week and still cant get his pH over 8.2! He has a 140g system I have a 40g system. I've done 1 small water change (10%) and started topping off with RO/DI water and my pH has already fallen to 8.2. I was going to do a 25% water change today but now I'm concerned that I'm going to crash my system.