Just an FYI...you're asking for trouble with four male dwarf gouramis in a 30 gallon tank. Gouramis are related to bettas and as such are EXTREMELY territorial with their own kind. Even breeding pairs must be separated when they aren't breeding. I know someone who had male and female siblings in their 55 gallon tank and they ended up having to remove one of them because they were too territorial and aggressive with each other. You will see one that is an aggressor and picking on the others. The others will start hiding and you will ultimately end up with three dead gouramis. I wouldn't even put four male gouramis in a 6 foot tank. There just isn't room for them to establish their territories (if you research gouramis in the wild, their territories generally cover an area of about 1 square meter, which is a little less than 3 feet). I would recommend rehoming three of your gouramis ASAP before you end up with dead fish. Also, especially being that your tank is a hex, there isn't that much surface area, so there's even less space for them to establish their territories.