All depends on what kinda of tank you have... Reef, Fish only, or Fish only with LR
Unless you have a reef tank you could get by with just tap water and some type of salt mix of ur choice. It's nice to use RO
water but it's not needed. Do your self and bank account a favor if it's not needed. Maybe take a water sample to a reputable SW
store and have the test your tap for nitrates and phosphates.
And for this bacteria bottle lol, got to love fish stores... Lol. Drop it! Go for a natural cycle, it may be long but it's worth it. This hobby requires patience. Anything less brake your bank account.
Hope this helps