I would not put even one of any of those eels in your tank if I were you. Not only will they get far too large, but they will eat your loaches. Waaay too small of a tank for even one of the eels.
Just lower the water level by a cm or 2 and you can greatly increase o2 saturation.
Or do a small, over tank, trickle filter and add even more o2.
Oh, and they do not add oxygen to the water... Just to be a smart ***, but they are just liberating the Carbon from the co2 and allowing the o2 to be used by fish... Just saying
Lowering the water docent mean that you'll increase o2 saturation you could actually be increasing CO2 saturation. If your pumping to much CO2 that will get over saturated as well. You just have to get the balance right. For the amount of water you have and the amount of plants and lighting. Plus using the right amount ferts plays into this as well. Just rial and error. Once you get this down for your tank your plants you should be good as gold.