I'm assuming by "dragon goby" you mean
Rhinogobius duospilus (see picture below).
These fish are subtropical, not tropical. When kept in tanks more than about 24 C they become very sensitive to low oxygen concentrations. In short, they begin to suffocate. When this happens they come to the surface to breathe the oxygen-rich layer of water.
You have three options:
1. Lower the temperature. There is a narrow happy medium of 22 to 24 C where these fish should be fine alongside most -- but not all -- tropicals. While some species, such as peppered cories and danios, do well at slightly cooler temperatures, other fish, notably angels and rams, tend to sicken and die.
2. Improve aeration / reduce stocking. Add an air stone to improve the aeration. Move the filter outlet so it splashes the water some more. The more water turbulence, the more oxygen will diffuse into the water. These fish live in streams, so don't worry about the water current pushing them about too much!
3. Remove the fish. Ideally, tropical fish stores would make it plain that these are not tropical but subtropical species. But since you have them already, perhaps removing them to their own aquarium would be an option. A 10 gallon tank would be fine, and you could perhaps add a few white cloud mountain minnows to keep them company.
Cheers,
Neale
PS. I used this species to mature my current aquarium. They're very nitrite-tolerant and make excellent first fish. In the wild they are quite tolerant of polluted water, which is one reason why they're still common even though they live in densely populated parts of China.
/www.thefishworld.co.uk/id184.htm
