Flow Rates in Sumps with Refugiums

Dom · May 25, 2017

A short while ago, I did a sump build using a 40 gallon long Aqueon which included a refugium in my build.

I understood (correct me if I'm wrong) that a slow flow rate was required in a refugium for it to be effective as faster flow rates reduce the amount of time for macro algae to absorb nitrates and phosphates.

But I am noticing a film developing on the surface of the water over the refugium. I've seen this before in tanks and just added a power head facing the surface to increase agitation. But I can't do that in a refugium; right?

Other than siphoning off the film or the occasional, manual agitation, is there anything else I can do?

saltyfilmfolks · May 25, 2017

Return rates have always seemed highly debateable.
In general I think a higher flow rate in a refugium should be better as, like any plant, it needs flow to process nutrients and uptake c02. IMO, it doesn't soak in when its slower.

Dom said:
But I can't do that in a refugium; right?

Yes you can. As most of my tank is DC, I just added a tiny 12v pump like one used in an ATO. ($4)

gcarroll · May 25, 2017

I agree with @saltyfilmfolks. There is no advantage to doing slow flow through a refugium. You can increase the flow, add surface aggitation, ect... without fear.

Dom · May 25, 2017

saltyfilmfolks said:
it doesn't soak in when its slower.

Yes, I understand that it doesn't work like a sponge. I just thought that the rate at which nutrients are introduced shouldn't exceed the rate of absorption.

saltyfilmfolks · May 25, 2017

Dom said:
Yes, I understand that it doesn't work like a sponge. I just thought that the rate at which nutrients are introduced shouldn't exceed the rate of absorption.

Understood.
I think a lot of people do belive that kinda though.
It would be hard to calculate uptake and introduction I think.

gcarroll · May 25, 2017

The algae will grow beat in the highest nutrient water. If the water is run slow enough, the fuge will have cleaner water than the tank. This is not what you want. You want the algae to always have access to the dirtiest water possible.