While moving rocks and installing new skimmer I lost about 4 gals of water. I added 4 gals of saltwater. Since water is removed and new water is added is it consider water change? someone said it can't be considered water change but didn't give me any explanation.
on a personal note i dont consider accidental spills and filling as water changes. its called an accident. i consider water changes as something i take out and put new back in, but thats just me.
technically 4 gal spilled and 4 put back is equal to 4 gal water change which in ur case on a 72gal tank with a 4 gal change is about 6% water change.
I don't necessarily think 4 gallons were lost. Part of that is used by the skimmer. But the end result is that new saltwater was added to the tank and it has a net effect of diluting any dissolved organics. If water evaporated, then fresh RO water should be added back to bring the salinity back to the original parameters, hopefully 35ppt.
I can't really believe this is a debate. Of course it is a water change. If I only read your title, then I would say "no" because it sounds like water lost to evaporation and replaced with fresh water. But saltwater removed from the tank and replaced with new saltwater is a water change. It might be an accidental water change, but it is still a water change. Does that mean you can skip a water change? I would say it is best to keep your normal schedule and just use this one as a bonus water change. Now I can't believe I wrote so much on this