[laverda]

There is o reason the tubing can not be on the outside, as long as the tubing is not opaque. The length of the tubing probably does not need to be 50’, but how long it needs to be is hard to say. If your feeding the reactor with oxygen rich water as in the skimmer compartment it will need to be longer then if fed from a place with little circulation. Conceivably you could feed it from under your sand bed and use a relatively short length of tubing as the water would already be low in oxygen.