making cement base for large rock
I have a large rock that I want to put almost vertical in a new tank and it would be too precarious to support with just more smaller rocks and substrate. So last night I mixed up some quikrete portland cement sand topping mix and set the rock in the position I want in order to create a stable base. Assuming it works and attaches to the rock securely, how long will the cement take to cure enough to put in with live fish.
On some forums discussing DIY backgrounds I've read that people will set it in water and keep making water changes until the ph is steady.
On one forum someone said to give it two months. I'd like to set this up in two to four weeks. If it would really take that long is there some other technique I could use like using spray foam and sealer?
I also saw that some thought adding salt to the water sped up the curing process.
Does anyone have any experience doing something like this?