Raise the pH of a solution and prevent build up of carbonates
How about $\ce{NH4OH}$? This does not for carbonates as readily, but it does form complexes with many metals. It depends on your intended use.

It might be easier to keep things away from the air:


Use a closed container.
Float an inert liquid (e.g. paraffin oil) atop your solution, or just a layer of pure water, which might take a while to mix.
Use an inert gas over the container to displace air.