What do you mean by toothless overflow wiers? I have a simple king of diy overflow setup on my 20l tank. It works fine so I guess it'll work on yours too. As for chillers don't stinge and just buy it. Firstly fans increase rate of evaporation and you will have to keep topping up water. Secondly they are ineffective and will only lower your water temperature by at most 10℃. On the other hand, a chiller can cool your tank below 15-20℃ your ambient temperature. Lower temperatures also reduce rate of evaporation. It's killing two birds with one stone! Happy fishkeeping! Sent from my SM-G570Y using Tapatalk