Hi Michael.
What are your water parameters? If the tank is only 2 weeks old you could have all sorts of things going on in there, so if you can get readings on your ammonia, nitrites, nitrates, etc., that might help.
As Left said, it is normal for them to come to the surface and gulp air, but if it suddenly started, something could be amiss. Oto's can be sort of delicate to acclimate, so that could be why they're affected and the shrimp aren't.
Since you already have DIY C02, you could try to do another water change without the Excel to see if that helps.
Keep us posted.
