well yeah that would be the best solution..but the sump is a 10g pierced filled with plants + rocks , placed higher than the tank so no overflow. Can't put much bigger sump there. There is still place under my tank, but i don't have a real good overflow..my customs were not really reliable and i can't buy one under 200 CDN $ . Tried on ebay but refused 'cause i live in quebec altough it mentionned worldwide shipping.
My next tank will be PIERCED.