I think, if I remember correctly, that Koko has one of these....
Eclipse tanks have the filter built into the hood -with biowheels. In the smaller tanks there is a well where the water runs over and through a blue flossed cartridge and over a biowheel. That is all the bio-base available for the beneficial bacteria to colonate.
This works very well for tropicals, but goldies need just a bit more.
Your little guys are not going to have a problem at all. But I think I would recommend that you get yourself a small container of some sort of biomedia of your choice - ceramic cylindars, sintered glass, lava rock, etc - place it in a bag and set that bag on top of the blue filter cartridge. There is room up there. The water will run over the biomedia, through the cartridge, over the biowheel and out into the tank. By pumping up the area that the beneficial bacteria can colonate, you will be able tosupport your fish even when they turn into big bruisers!
An Eclipse is a pretty tank. As noted above, use only acrylic rated cleaning pads on it. Other than that - enjoy!