The bloom first - if it is white, it is a bacterial bloom (green blooms are algae). These are different bacteria from the ones we want to grow in the filter; they live free floating in the water and multiply very quickly. We see the bacteria as the mistiness. The bloom bacteria live on organic chemicals, and there are plenty of those in a new tank - the plasticiser leaching out of all the new plastic things; chemicals in the corner sealant etc. It is impossible to get rid of the bloom as they multiply faster than we can get rid of them but once they have eaten all their food supply they will die off. Because every tank is different, it is impossible to say how long this will take.
The bloom itself is not harmful to fish, but the bacteria do use oxygen and are in competition with fish for this. Make sure the filter outflow is circulating the water well (ripples on the water surface) to encourage maximum gas exchange - oxygen getting into the water.
Although fish gasping at the surface indicates not enough oxygen in the water, it is also a symptom of ammonia and/or nitrite in the water.
With your ammonia levels, water changes are a must. You must keep it below 0.25ppm, and when you get nitrite, that too must be kept below 0.25. If necessary, you can empty almost all the water leaving just enough depth for the fish to be able to swim upright. Yes, it is stressful for the fish but swimming in ammonia is worse. Provided you dechlorinate the new water and warm it to the same as the tank water the fish will not suffer. You need to do this as many times as necessary to get the ammonia down below 0.25; wait half an hour after the first water change to allow the new water to mix with the old, then tst again. If it's still above 0.25, do another water change. Test again after half an hour, and if necessary do another water change and so on until the reading is below 0.25.
While you are waiting for the half hour before the next test, read
this. It explains what you need to do to keep your fish alive.
Ammo lock and similar products convert the ammonia to a less harmful form, but the effect only lasts about 24 hours. Our test kits cannot distinguish between the toxic and non-toxic forms so your reading will still show quite high after adding the ammo lock. This is only a temporary fix; the effect wears off quickly. Water changes are a much more effective way of controlling water conditions.
Try feeding the fish less. Less food = less ammonia. Feed them once every two or even three days until you get the ammonia under control.
You have 6 tetras and 3 cories now. Can I ask what tank size they are in? The smaller the tank, the faster the ammonia level will go up.