Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Nitrifying bacteria need the carbonates, it is where they get their carbon. I would raise the KH as high as you can to improve the growth of the bacteria. Absolute minimum of 3 degrees, and something closer to 10 degrees if possible. Won't hurt the plants unless you have some of that awkward group the really demand the softest water. GH of 4 is OK, if you can raise it a bit that is OK, too.
These bacteria were initially identified in the lab in cultures where the water was like liquid rock: Very high GH, KH, pH and TDS.
No salt, but plenty of other minerals. I would add plant fertilizer like KH2PO4 and trace minerals, too.
After the cycle is done you will be doing some really big water changes to get the NO3 way down. You can use softer, low TDS water for this refill. It is when you want the bacteria to be growing at their fastest that you really need to meet their needs the best you can.