Pros and Cons of using an underflow

[Lota Reefer]

Hi R2R,

Am in the planning stage of a new build, based on a nano sized, SPS dominant, barebottom tank with sump.

Came across the idea of using the weir wall as an underflow and overflow method of getting the display tank water to the sump filtration.

As I understand it the underflow means the back wall is two pieces of material that are offset (height. Front is slightly higher, so it does not rest on the base, ergo detritus passes under it, and the back piece is lower) and the two pieces are spaced apart. This creates a channel where the water passes under peice 1 up between the two and over the top of peice 2, all the while peice 1 also has a typical comb weir to surface skin.

The idea is less maintenace, being a barebottom some detritus will get sucked up the underflow and the floating bits still overflow, so I have a cleaner looking DT.

Does anyone have experience with this method?

Are there known pros and cons?

Resources for fluid dynamics...I take it the wider the space between the two pieces the more flow required? Which could be problematic for 3 to 5 times turnover...

Is this a bad idea...why isnt it more popular on paper it makes sense...

What do you think? Know...

 

[madweazl]

Typically, proteins and other nasties will collect on the surface of the water and the overflow will slough these off and down to the sump so they can be collected by a filter sock and/or skimmer. Strong flow within the tank can typically keep all of this suspended in the water so it could be removed regardless but that is typically why overflows are used. Detritus is kicked up by the same pumps so it could be removed by the overflow. On another note, adding panels within nanos eats up valuable space; your underflow may take up more of that precious space than an overflow. Just something else to consider.

One more thing, SPS are pain in small tanks. Once they start growing, they grow fast and require a lot of trimming. I started off placing them pretty close together (within six inches) and it has been a giant pain. I wouldnt suggest placing any of them closer than about 10" to anyone now (that still only gives them a five inch radius to grow into).

 

[Lota Reefer]

Thanks for the tips Madweazl. I sure hope my problem will be overgrown SPS! Look forward to that...I think. But points noted...give room to grow.

I hadn't thought too much about the space...good to consider if the sacrifice is worth it.

Having the flow kick up the detritus should work, however reading of experiences of hobbyists using barebottom, enough comments caught my attention that many seem to be satisfied with bits collecting into areas which they say makes it easier to syphon out...so was thinking the underflow might accompany the maintenance rhythm.

 

[madweazl]

Pick bare bottom because you want to, not because you believe you need to. There are successful SPS keepers on both sides; anyone that tells you one is better than the other is fooling themselves.