Inital Fill - Tap Water Okay?


New member
I understand it would be best to initially fill the tank with RO/DI water, but would it be a huge mistake to fill the tank with tap water, add salt, and then cycle the tank? My tap water has a TDS reading of 6-7.

Or should tap water be used to leak test everything, drained, and then fill the tank with RO/DI, add salt, and begin the cycle process?


New member
If your TDS is 6-7, then I don't think you even need to use an RO/DI ever.
However, sometimes the city cleans the pipes and add a bunch of chemicals, and it is sometimes thought that conditioner can raise the TDS by a lot.
I you already have an RO/DI though, then you should just use that to fill it. Better safe than sorry!:)


Staff member
RC Mod
Ro/di would be my advice, to save work and expense later. The reason primarily is phosphate, although tap water can have really bad things in it that a conditioner won't even touch. Your rock and sand will import some phosphate anyway; but there are some far more exotic contaminants to worry about---especially if you live where there were a lot of mines or industry.