Stop me if this is old news. I'm not too familiar with the Eclipse systems, but if they are like the small acrylics tank I have had, it sounds like a common problem I've run into. The top black rim of plastic can often act as a syphon in some areas, and will continue to 'leak' until the water level drops below the lower part of the rim. I thought a couple of my tanks were cracked until I discovered this. Silicone should work to stop this, but I have never actually tried it.
My quick fix is to simply pop the rim up to break the syphon. The syphon shouldn't start unless the water level gets rather high, so I try to avoid these situations that way. I suppose another solution might be completely remove the top rim and drill small holes into it to avoid a syphon starting, but this is also unproven.
Hope this helps.