I have always been loyal to Seachem Prime for all my top off water. Recently realized I have been using it incorrectly for years...I would dose my tanks immediately after doing a water change. Problem is that Prime eats up metals so my iron dosing was probably very inefficient. Up until recently I have had really good tap water, moved to Florida and you can forget about it. I started using distilled water from Walmart and it worked fine, used it for a year until I noticed a shrimp in my pico tank go crazy when I did top offs. It finally hit me that distilled water is acidic, so I switched over to Walmart spring water which has a much higher pH. It comes from a crystal spring within FL so I am getting some natural trace elements, it is processed with a micron filter, a UV light and ozone. Is there any need to continue using Prime if I am only using spring water? Only thing is I do run my water for a long time on top offs before doing a water change due to my heavy plant load and light feeding practices, so the only thing I really have to watch is my TDS...which I will be honest, I dont. I only keep enough clean up crew to break even with the growth rate of algae so that I do not have to feed them regularly, and I am strict with proper fish feeding. I use Purigen as well, so cosmetically there is no reason to change the water either. When I vac every 6-8 weeks it lowers the TDS a bit I would assume.