While looking on the internet for chelated iron I also found chelated magnesium. I wonder how different this is compared to using epsom salts?

I have a little problem with one of my citrus plants... the container it is growing in appears to be the home for an ants nest. I don't think the ants are a problem for the tree. They do cultivate some aphids when they are "in season" but other than that I think they leave the tree alone. The issue is that I have to take the tree inside during the winter season and I don't want to take the ants nest inside with it.
The ants nest was probably already there during last winter as I occasionally found an ant running around on the floor. I just didn't realize where it came from.
So I want to get rid of the nest. I already replaced the soil as much as possible last spring but that apparently didn't stop them. Last weekend I tried drowning the ants by completely submerging the container in water for an hour or so. They survived! There must have been some air bubbles left behind in the soil so they could keep breathing...
What else could I try? I don't want to poison the soil of the plant...
My next step will be to put an ant trap in the container. I'm just not sure these traps are really effective. If the ants aren't gone by the end of the season I will again try to get rid of them by replacing the soil, and this time also by rinsing the root ball with a water jet. Is the ants do return after that, I won't take the plant inside again. And that would really be a pity as it is one of my nicest growing citruses!