Raise the pH of a solution and prevent build up of carbonates I need to raise the pH of a solution so the easiest approach is to add alkali hydroxides (NaOH, KOH, etc). But as most of you know, the CO$\ce{_2}$ in the air can react with these hydroxides to form carbonates which usually  precipitate out the other metal ion dissolved in the original solution. So what else are my options?
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.