I read on another forum that the optimum rate is 1.5 - 2 tuurnover rate of your tank volume through the filters. This will give you the best contact time of your water through your biological media in your filter.

Do people aim for a certain turnover rate in their tanks???

Nope , i dont anyway , as long as it aint too fast, as it wil be more effecient that way

it either goes through faster & more often ....or slower & less often, as long as it is not extreme ie 1x/h or 10x/h, I am unconvinced that it makes any diference, contact time vs contact frequency. 2x-6x/h should not be a problem from filter or fish perspective.

Slow flow almost guarentees that the water leaving the filter is 100% processed, but because of the low flow rate the water in the tank is slightly more poluted at the inlet (compared to a higher flow system). Higher flow means a slight risk of not 100% processing (ime you need severe polution & very high flow to actually do this on a mature system...I tried it on some culls 5000l/h pump on a 100 gal system & very heavily overfed. & still had no nitrite/ammonia) but that the water in the system is "more evenly" poluted....& bear in mind we are talking minute amounts not detectable on a test kit. there is ammonia in any tank that contain fish...there must be because the fish excrete it ,,,but in a mature system it is not detectable because it is processed rahter than left to build up.