If it helps 'coolie' loach is kuhli loach. Having the the real name will help you find out more about them.
If the tank has only just been set up, it will take a while for the fish to settle in and get comfortable in the new location. Once they do, I'm sure you'll see them up and around the entire tank. Upping the number of fish in the schools will help them gain confidence as well. I've heard glassfish in particular can be very scattery and scaredy without decent backup.
As has been mentioned, the stocking is rather odd. The best thing to do over the next little while is researching all the fish in there, and settle on what type of tank you want to set up ie African cichlids (with the yellows and lionheads as your base), or tropical community, etc etc.
500L is a great size tank! And your scape for the tank looks really good. If you went with tropical community, you could swap the plastic plants out for real ones.
Just to check, I'd put your thermometer at the opposite end of the tank for a while, to see if the temp is different down there. If it is, I'd recommend putting the heater more horizontal in the middle of the tank (you could hide it with the driftwood and run the cord under the substrate to the side of the tank).
Do you know how big the filter is?