If you are changing water, i.e. taking SW
out of the tank, all of the water you put back in needs to be SW
, unless you are attempting to lower your salinity. But there is not much benefit in terms of the issues you are seeing with NH4 and NO2
in doing a 7% change. It will have no discernible impact. More effective would be a large change tomorrow, and another large change a day or 2 later. If you match the SG
and the Temp, it won't hurt the tank at all - and it will drastically cut the levels of NH4 and NO2
in the tank.