Hi, Duckman, and welcome to the forum!
You can use the sand that's in the filter--enough bleach will make it clean again--but I think in your position I would replace the sand, and here's why:
1)You're filling with nice, clear water, and I wouldn't want to take a chance on blowing black, foul-smelling water into my new pool. The 1.5 hp pump, if it is truly 1.5 hp, is a big pump for that filter, and may well have a tendency to push stuff through the filter. I'd hate for you to have to watch that nasty water blow back into your nice, clean pool! (By the way, whichever way you go, make sure when you start it up for the first time, that you prime the pump and start it up in backwash mode so all the junk in the pipes and sand goes out into the yard, rather than into your pool. After the backwash water is clear, then switch to rinse mode for a minute or so, and THEN switch to filter. You only make that mistake once...ask me how I know)
2) In moving the filter, there's a possibility that some damage occurred to the laterals, and if that's the case, then it's going to start blowing sand into your pool when you fire it up, which you don't want. Replacing the sand would give you a chance to inspect and replace any broken laterals before you get the pool up and running.
3)You will know for sure that it's the right sand--playground sand, sandblasting sand, etc is not the appropriate size for a filter, so you want to make sure it's the right stuff, and
4)You will know what is in the pool. Unless you know what chemicals they used, there could be a mystery combination of goop from chemicals in that sand, and you don't want any of that in your nice, newly-filled pool.
Your choice...but I would bite the bullet and change it. It's labor intensive, and not a really fun project, but it's not very expensive and can save you lots of time in the long run.
Congrats on the new pool!!
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