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Rear sump in tank

zoon

Member
Joined
25 Jul 2010
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123
I have a Fluval M90 reef tank that I am modifying to be a planted tank. It’s 136l and had a rear sump similar to a Fluval Flex, but on a much larger scale. It has 4 sections and I have modified the baffles a little to correct the flow through them. I have the original return pump, but it is really small and I can’t find any info to show how powerful it is. I am going to have the first section of the rear filled with various grade foams, the second and third filled with alfagrog and the pump and my heater in the last.

Went to lfs today and they advised going for 600lph return pump and a circulation pump in the tank.

I was planning on an Eheim CompactOn 2000lph as the next one down is 1000 with nothing in between, but they do have adjustable flow so I can aim for around 10x turnover per hour.

Guys in lfs said I’m stuffing so much in the rear compartments that a more powerful pump will empty the sump faster than it can fill so it will dry out. They said I’m better off with a smaller power pump and a circulation pump in the tank to give me the flow I want. I was aiming for a 10x per hour turnover through the sump, but what they’re saying makes sense so now I’m confused - what shall I go with?
 
Hi all,
Are you adding CO2? If you aren't you need much less flow.
I have the original return pump, but it is really small and I can’t find any info to show how powerful it is. I am going to have the first section of the rear filled with various grade foams, the second and third filled with alfagrog and the pump and my heater in the last.............said I’m stuffing so much in the rear compartments that a more powerful pump will empty the sump faster than it can fill
I think they are probably right.

cheers Darrel
 
If it’ll run your sump dry, then it’s a no brainer. If you really need 10X flow (only if you’re injecting CO2) then pop another pump into the tank itself.
 
If it’ll run your sump dry, then it’s a no brainer. If you really need 10X flow (only if you’re injecting CO2) then pop another pump into the tank itself.

I’m not sure if it will run the sump dry, that’s what I’m trying to figure out

will having two chambers of alfagrog slow the flow that much? An external stuffed full of alfagrog works fine, so I figured the rear sump would work similarly. Is two chambers of alfagrog overkill?
 
The tank is in a spot where having an external filter isn’t possible, hence the revamp of this old marine tank
 
It’s physically impossible for an external to run dry though, it will just have slow flow. A sump will have slow in and through flow, fast outflow and hence potentially run dry.
 
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