Refugium Flow

[CoryDude]

How much flow are y'all using in your refugiums? I'd originally thought about using a very slow pump, but after searching some previous threads here, I'm thinking about increasing the gph. I've got a larger eheim that can do 300-400 gph.

I'm also assuming this rate would be safer since there will be an anaerobic area in the fuge. Wouldn't a slower flow have the chance of producing anoxic zones under the fuges's sand bed and releasing hydrogen sulfide?

I'm also seeing that cheato needs some kinda of direct flow to stay healthy. Would a power head in the refugium defeat the purpose of a safe area for plankton and pod production?

[ErikH]

Slow flow through your fuge is what is recommended, although too slow of flow can cause your PH to ride high due to poor oxygen exchange.

[Europhyllia]

PH to ride high due to poor oxygen exchange.
interesting my assumption would have been: high CO2/low O2 = lower pH

I think if your sandbed is of sufficient grain size and depth there will be anoxic zones no matter what the flow above is.

My current return pump is 630 gph. future return pump will be around 950 I believe.
I used a 1200 before and that seemed a big much. I think the 950 will be perfect for my set up

[allan]

I have three pumps feeding my display and frag tank. One Rio 3100, Rio 2100, and a Quiet One pump (frag).

Additionally I have a little petsmart power head in the sump for some additional flow to some dead areas... fixing to put a K3 down there and tossing the little power head in there.

I believe that the zone under the sand bed is a desirable thing. I spoke with Ping at length concerning that very same issue and he hadn't experienced any of the bubbles. But later I had another conversation with him where he had removed (or maybe he was planning to remove) the DSB in that tank. You could see the dark line on the side of the glass where the "zone" was.

In my opinion you need good flow and lighting to get your chaeto to grow (macro in general). Not crazy flow, but good flow nonetheless. I don't think you experience the full positive effects of a DSB with more flow though.

[Europhyllia]

I don't think you experience the full positive effects of a DSB with more flow though.
Why?
So much of what makes the DSB special is happening a few inches underground -away from flow.
I had a DSB in my 125 and am planning of having another DSB in my new tank.
I have the DSB in the display (not the fuge) and definitely have had a pretty good flow there.
Didn't affect the anoxic areas at all.

After the tank burst and I removed the sand I had plenty of areas that clearly hosted gases and bacteria commonly found in anoxic areas.

[allan]

I don't know, help me understand this.

I thought it was the slow flow over the sandbed that causes the exchange that I guess you're talking about. Uneducated folks like me would say, bad stuff sinks to the bottom and out of the water column. It was my understanding that a faster flow would not allow much of the exchange to happen, so faster flow less exchange, to maximize the benefit the flow should be slower.

Obviously the process would never happen if the flow is several thousand gph, and what you're telling me is that 100 gph is not enough. What's the formula that will tell you exactly what GPH would be most beneficial.

[kkiel02]

I use a mag 9.5 for my 45 gallon sump/fuge that is my return to the displat. My next sump will allow me to control the flow between the sump and fuge seperately so I am much more excited about it.

I thought Ping said for a dsb to be most effective there should be no macro but with high flow to help move the water through the sand?

Also my chaeto and caulerpa dont get direct flow. It just grows as a mat at the top of the surface which actually helps to keep my salt creep down.

[Europhyllia]

here you go:
http://reefcentral.com/forums/showthread.php?t=1652103&highlight=dsb+anatomy

[Ping]

A deep sandbed works best if it has high flow for advection. It should not have vegatation or long term rocks on the surface for proper advection to occur.

A vegatative or rock fuge should be a shallow 1 inch or less sand bed. In my vegatative fuges the flow is dialed down to whatever will prevent the overflow of the tank having a 1 inch overflow tube. If there are no crabs or snails, the bacteria on the vegatation and the sand, as well as the pods, will keep the fuge clean and productive.

[Ping]

Also a display DSB set up to meet the demands of specific animals (Gobies and others) does not equate a fully effective DSB.

[ErikH]

Karin, I thought the same thing, but I read it's just the opposite. You don't get enough co2 into your water which keeps it too high. Hold on Ill post a link....

[ErikH]

"As discussed above, a reef aquarium's pH rises when its water becomes deficient in carbon dioxide. In practice, this deficiency can be caused in several ways. The diurnal (daily) change in pH in reef aquaria occurs because of the biological processes of photosynthesis and respiration. Photosynthesis is the process whereby organisms convert carbon dioxide and water into carbohydrate and oxygen. The net reaction is:"


http://reefkeeping.com/issues/2005-03/rhf/index.php#6

[ErikH]

essentially you want the offgassing co2 from your macro to stabilize your PH diurnally as well.

[Europhyllia]

That's very weird! On his Causes of LOW pH he mentions high CO2.
And isn't my macro supposed to put out O2 -not CO2?

[ErikH]

During the day co2 offgasses and at night macro uptakes co2. That's why macro doesn't grow as well on a full 24 hour cycle...

[allan]

Okay Erik, now I'm lost.

Because of the reverse cycle most fuges are on for the stabalizing effect of the PH I'm thinking that you are meaning this...

When the Display tank goes nocturnal, the fuge goes diurnal... or when the lights turn off in the DT, the fuge turns on. So while the lights are off in the fuge the macro is doing it's offgassing of CO2? (who'd a thunk it?), and when the fuge lights turn back on (DT is off) the macro begins the photosynthetic part of its day (Diurnal) and puts oxygen back into the system?

The way I always understood Diurnal and Nocturnal is to describe the circadian cycle of particular animals and plants. By that description both the DT (or the majority of it's inhabitants, definitely not all) and the fuge (by this I mean strictly the algae) are diurnal. We off set the fuge light cycle to stabalize the downward swing of the PH during the lights off period of the DT.

This is where I'm a little confused, when you say day, are you referring to your day, your DT's day, or the fuges day?

My head hurts. :)

[CoryDude]

allan, you me an imatrex for the migraine I'm getting from reading your post.

So after reading this (thanks so much for the discussions so far) I'm thinking about splitting my overflow return to supply the fuge. That would be about 400gph into a 29 gallon tank. I never thought about the extra co2 uptake by the plants. That coud benefit my bacteria filter since co2 is byproduct from it.