Thanks, they were quite cheap from what else I've seen around
This isn't necessarily true, trickle filters are very efficient at gas exchange, which when you are low tech. is actually an advantage. If you don't add CO2, normally during the photo-period the water will have very low levels of CO2, because it is continually depleted by photosynthesis. The water will be fully saturated with oxygen via the same process. If you have a large gas exchange surface that CO2 depleted water will re-equilibrate with atmospheric levels of CO2 more quickly and CO2 is a relatively soluble gas .I ask because your sump wont be at all suitable for a low tech as there is so little Co2 available in a low tech, what there would be, will in fact be gassed off down the overflow
OK then I am obviously wrong so get going with them water changes & overflows & trickle filters & let me now how it goes!