Hi Sakkie. I think 150 litre for a settlement chamber is too small-the water will pass too quickly, no chance to 'settle'. I would suggest to use the first 2 drums from the bottom drain for mechanical filtration(filled with brushes or other filtermedia), the next 2 for bio convertion, and to add another drum at the end to put the pump in. From that last 'chamber', you can return the water to the pond through a UV, and maybe then a bakkieshower or waterfall. Just my opinion. Check this forum for all the info you need. To kickstart the bio, it will help if you can obtain some mature media from a koifriend. Other suggestions can also be viewed on this forum. Good luck, and enjoy.