When I do a wc I add nutri ocean water. The water is already mixed with salt with and prepare . So I dont have to mix n process saltwater . The hydrometer salinity level was really high so I had to put ro water.. ( not mixed just water in the tank).
It sounds like the op (please correct me if I'm wrong, op) is topping off with ro and doings wc's with sw.
OP, just to clarify for you:
Water changes are a replacement. When you take out 20% of the water, the tank salinity is still what it was before you took some water out, there's just less water of that salinity. Salinity is basically measuring a ratio of water to salt. That ratio stays the same until either more salt or more freshwater is added. When you take 20% of the water out, you have to add that water back and it MUST be saltwater with the same salinity as the water you took out. The water you take out is saltwater, with a certain salinity, therefore you have to replace it with water of the same salinity.
Top offs are an addition. Water evaporates from the tank, but as you know salt does not evaporate with the water. Therefore, the only thing you need to add is the water that evaporated, which is RO water. Never top off with saltwater, because saltwater is not what is missing. You need to add RO.
Another problem is 100% WCs. First of all, it is not necessary. 10% water changes once a week is enough, and is a lot safer. The second problem with 100% water changes is that it is extremely difficult to accurately reproduce the same conditions in your new water as the old. It isn't so simple as just dumping out he old water and dumping some ocean water back in. This will kill your fish, if not immediately, over time. There are factors like ph, temperature, salinity, etc. that NEED to be very similar if not exactly what the old water is for the 100% WC to be safe. Even then, it is a much larger task, and an unnecessary one at that to remove all the water from your tank. I highly recommend doing smaller water changes on a regular schedule.
Sorry for the wall of text, but please read it OP, it's really important stuff I've learned from the other users here on AA, condensed into a few paragraphs.
