ok i'm pretty sure i've read this on here somewhere but for the life of me can't find it again.

within the next couple of weeks i will be moving my tank to a better stand, and when i do this i will be removing the gravel i have in it now and replacing it with sand, which i have learned is easier to keep clean rather than gravel.

now my question is, how much of the original tank water do i need to keep for when i refill my tank?

i know this is important in keeping my o's healthy, so i want to do it right.

just think how much water do you usually remove during
water change? that is your first option.

moving the tank with water is dangerous, so i suggest you can save
50% of it in a container and empty the tank before moving. then use
the save water as your seeded water for continuous cycling. just make
sure your filter pump is running, either in your container or in your
tank to keep good bacteria alive. then, your new set up will be fine.

thank you very much Paul for your quick response, it is very much appreciated.

Your filters will also have the bacteria you need in them. I don't envy you having to move a established tank.