Skimmer and canister filter in the same loop

[Steve]

Considering adding a external skimmer to my system and thought about using my canister filter (450gph) to feed a skimmer/20g sump and then add a 450gph return pump back to the tank. 180 gallon tank, 200lb sand bed, 200lb live rock. Are there any issues I should consider.

 

[Jeff]

If you are using the canister filter first before going to the skimmer, you'll be using up filter media much faster than if you had the skimmer first in the loop. The skimmer will take out the bulk of the garbage and most nutirents, then the canister filter will polish the water from there with carbon or whatever your chosen chemical media would be. Don't use the canister for mechanical filtration (floss, bioballs, ceramic rings, rubble, sponges...) it'll frustrate you with how often it'll need to be opened and cleaned and can cause buildup issues too.

 

[Steve]

If I go with this setup I would use a multi level float switch in the sump as a safety check on the water level by connecting 1st the pump from the tank, 2 the skimmer, 3 the canister filter pumping back to the tank. If either of the 2 pumps failed and the level dropped down to 6 inches or increased to 10 inches in the sump all 3 devices would lose power, thus not flooding or running dry. The risk would be if the float switch failed along with a pump. I would set the pump level from the tank to break contact with the water before overflowing the sump as a safety backup. The worst I can in vision are the pumps running dry. All of this to avoid a Weir on a DAS tank, any thoughts or suggestions.
Thanks
Steve