I don't know how bad it is, but it's certainly not good.
If it's heavy enough to trap bubbles, I doubt there is much gas exchange going on.
For now, you may be able to manually skim it by dipping a container in and letting just the surface water flow in. It will be a bit tedious, but you should be able to remove most of it that way.
To prevent it, you will probably need some sort of surface skimming attachment for your filter intake, or pretty heavy surface agitation (so that it gets mixed into the water column and picked up by the filter).
That's a lot. Remove it by skimming off the top layer of water with a cup, or container. Just submerge until water runs in slowly. When done top off with fresh water.
What type of filtration and water return are you using now? You need to increase surface agitation. I do that by simply turning my spraybar upwards so the outflow disturbs the surface. You can also add a powerhead or circulation pump. Whatever method you choose, the sum will diminish.