hej janne som jag förstår det så är det inte så i zeovit, enligt deras manual: The mulm, released from the ZEOvit® material, contains bacteria that are used as food by the corals. We therefore recommend placing the ZEOvit® filter after the skimmer in the last compartment of the sump. This is very important because it provides nutrients to the animals. This procedure has a very positive impact on colors, polyp extension, and vitality of the corals. //fredrik