Flyfisherman said:
The reduction in flow rate for this filter when fully loaded with media is unbelievable "a drop in flow of 950lph", i think some clarification is needed. No wonder I am having problems if this is right.
Paul, no clarification is needed. The 10X rule is based on this principal that filters lose 50% or so of their flow. The flow loss is simply due to the friction and blockage of the media. When manufacturers rate their output it's with an empty filter and very little pressure head. The ratings are therefore optimistic at best. This is why the rule specifically calls out a 10X "Rating". Whatever a filter is rated at we discount that by 50%. Having a 10X filter "rating" means that the actual turnover in the region of 3X-5X the tank volume.
Instead of trying to figure out each filters actual turnover, which will vary as a function of media type and volume, and will also depend on how far below the water line it is sitting, it's simpler to use a generic 10X calculation which get you where you need to be.
Cheers,