I did a water 45 gallon water change today, and the ORP went down even when the VC is added a pre mixed for several hours prior to changing.
I have noticed that the ORP seems to go back up a little faster than the 1st dose. The skimmer did not go crazy on either dose. That's a good thing.
I use Instant Ocean, and have for years. I don't have to add anything to it, but I try to get the water as close to the tank water as possible as far as calcium and alkalinity.
My calcium runs close to 500 and alkalinity is around 9. Instant Ocean does not run that high on a new mix. I don't mind adding a cap full or so of the two part solution to boost it up some.
I feel a change in salt would be more detrimental to the system than adding a little to part to it. I have thought about buying some Reef crystals to mix with Instant Ocean, but changed my mind.
I was just trying to match the VC level a little to match the tank water.
Trying to avoid a sudden change in the tank water. It really did not make a big difference so I will probably continue to add to the sump, but I will also continue to add to fresh saltwater also.