how long is too long?
 

This question has a couple different parts to it. This may seem a little strange, but I have a question regarding how long water can sit in a tank without fish or live rock.

Ive reached the point in my freshwater to saltwater conversion where i am ready to clean the sand and start mixing RO water to add to the tank. I have a 75G and will be mixing approx 20-25G of water at a time, and add it to the tank after placing the sand in. The thing is that it will take me probably 2 days to get enough water from my RO unit to start up all the pumps and skimmer, so is there going to be a problem with the salt settling out or anything?

after gatting everything running, if it ends up being a month or more before adding live rock, will this be detrimental? as well, after adding live rock, what needs to be done to maintain it between adding fish and inverts?

Sorry if this sounds like a newbie question, but i am a SW newbie =)

You won't have any problems.

If you have not done so, fill er up with fresh water first and run all pumps etc.
This is to check for leaks, before you spend the expensive salt.

I was planning on putting the sand in first and filling it after, is it ok to mix the salt in after? or is there a way i should add the sand after its mixed?

Most of the problems adding sand is when you already have livestock in the tank. It shouldn't be a problem adding sand then water or the other way around in a new setup. It will get cloudy but it will settle down eventually. Adding fresh water first then adding the salt after filling it or adding a saltwater mix is not an issue either. It really is a matter of preference.

ok, thanks for the help. The last question i have is will there be any problems with any bits of algae left over from the freshwater setup, or will they die off after the salt is mixed?

id clean the tank well first but thats me why start with problems already
but yes the algae will die leaving PO4 headaches ugh clean the tank

the tank has been thoroughly scrubbed with a vinegar and water solution, and rinsed many times. I will be rinsing again with RO water before i fill it. The only remenants of algae i cant remove are a couple pits in the bottom glass of the tank, a tiny bit in the hoses of the canister filter, and the tiny bit that has managed to get behind the silicone in the corners. It is so little that i dont think it will be an issue, but i thought id check first.