Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
The nitrifying bacteria in fresh water tanks will grow just fine in water with a wide range of parameters.
Oxygen: High oxygen level, good water movement.
Ammonia: up to 5 ppm is OK, and 3 ppm is a good level to maintain while doing the fishless cycle. After that, the bacteria will grow or die to match the ammonia load from the fish.
Nitrite: Up to 5 ppm is OK during the fishless cycle. Higher levels of NO2 are associated with slower growth of these bacteria, and the cycle seems to stall.
Carbonates: These bacteria need the carbon from the carbonates. If the KH is at least 3 German degrees of hardness, there is enough carbonates for the bacteria. Monitor it. If the KH drops add some carbonates or bicarbonates.
pH: I am not sure if these bacteria specifically need alkaline pH, or it is the carbonates they need, and a good level of KH is usually associated with alkaline pH. Anyway, pH down to about 6.5 is generally OK, though they are starting to grow slower at that lower end. By 6.0 there can be a serious problem with these bacteria.
I have often set up a new tank by sharing some media from the filters of several other well established fresh water tanks, no matter what the water parameters are. Salt water tanks have different species of bacteria, so these are not useful in fresh water tanks. But no matter what the KH, GH, pH or TDS, fresh water tanks all share the same bacteria, and the bacteria seem able to make the switch just fine.
In this case I would take no more than 25% of the media from each of your established tanks and put this into the new filter on the new tank. Then do the fishless cycle.