Flow Under A Reef - Who Cares?

[Tiggsy]

Calm down calm down ;)

Please ignore any comparisons with my old "mature water, who cares thread?" :P

I am about to loose a fair amount of under reef flow via some mods to my tank.....and i am curious as to the down side of this. I have read LOTS on various ways to elevate reefs and closed loops etc, etc so its clearly regarded as a big deal....just wondering why? or more important - will the neagtive affect be an issue?

I assume flow through LR can be so poor at the base of a reef that it cease to provide usefull filtration...that would make sense and i hope to counter that via a much larger volume of well used LR within my sump (an amount far greater than would be lost due to poor flow in the main tank)

I also assume junk would collect down there - and heres where i dont really get it.....if junk collects is it not as simple as critters will break it down and whats not broken down just becomes inert....aquatic "soil" as it where?

Im sure theres something im missing so my question is- low flow under a reef....what downsides to i need to counter via the rest of my system or are there down sides so drastic that no fancy sump will save me? :o

T

[kim]

Originally posted by Tiggsy@Dec 8 2005, 23:14
I also assume junk would collect down there - and heres where i dont really get it.....if junk collects is it not as simple as critters will break it down and whats not broken down just becomes inert....aquatic "soil" as it where?

I think that's the main point.

You could (after all) throw a 3/4 pounder with fries in your tank and the critters, and then the bacteria, would lunch on it. Including the cyanobacteria, of course.

But would you recommend it ? B)

Detritus is a fact of life. The key is not to let it accumulate too far.

In some tanks that's accomplished by a DSB. That has more detritus processing power than LR because sand-based critters have evolved to thrive on detritus more effectively than the rock dwellers. Why ? Because in nature detritus settles in the same place as sand....just like sand it doesn't settle on the rocks in a reef(too much flow).

As a result, rock based life tends to be more carnivores and filter feeders. Yes, that's a generalisation....but broadly true. Sand-based life, in contrast, can't filter feed very easily, there's (comparatively) slim pickings for carnivores but in compensation, a lot of crap. They grow to deal with it.


Since in a reef, detritus doesn't settle, people tend to mimic this by siphoning detritus themselves, or have such flow that it is re-suspended in the water (which is what you propse to eliminate).

Compared to true reefs, our tanks are generally low in particulate organic matter such as detritus (which is suspension filter feeders love).....but very high in terms of dissolved organic matter (which some inverts love, but we almost inevitably have too much anyway). Allowing detritus to sit and rot just exacerbates this reversal. It just degrades water quality with dissolved organics, adding to the biological load on the tank, whereas re-suspended detritus could in fact have some use (in moderation !).

Whether all this is disasterous or not depends on a whole lot of other stuff of course....how much filtration, how much stocking, what kind of stocking, blah blah blah. So there's no clear answer, just a few vague concepts.

Just thinking aloud.....it's the forum for that, I guess.

kim

[stan.the.man]

Originally posted by kim@Dec 9 2005, 00:07
Just thinking aloud.....it's the forum for that, I guess.
kim
Thank goodness for this forum and people like you that take the time to answer in such detail. Brilliant.

Stan

[Tiggsy]

Great answer kim.

so my main issue would be potentially having to deal with excess disolved organics.....which is not to bad- i was worried that something could "develope" in that situation that is hard to counter (while disolved organics are an issue at least its one we know how to combat)

[wayne in norway]

My other issue is that if you had a bunch of gak accumulting under your lr it will start to 'choke' the pores of the live rock. Blowing water around slows this down

[Tiggsy]

Originally posted by wayne in norway@Dec 9 2005, 12:06
My other issue is that if you had a bunch of gak accumulting under your lr it will start to 'choke' the pores of the live rock. Blowing water around slows this down
yes, i suppose this relates to my first issue that the LR will be less useful at filtering.

i am content that i will have ample LR in my LR sump for filtration.....my issue was soes some sort of evil "toxin" build up in the gunk that i cant handle - sounds like it just pushes the bioload up a little which i can deal with.

[JasandJules]

Would there also not be an issue of an area (assuming the rock is on the sand) becoming anoxic (sp?) and then if someone burrows under there it will release sulphur dioxide?

Also the added issue of simply reducing the effectiveness of the filtration? Why not put the LR on a small bit of reef rack in the sump, and run a powerhead underneath? This can then blow all the c*&p into an area for you to syphon out?
That is what I have planned for one of my tanks.

[Tiggsy]

"becoming anoxic (sp?) and then if someone burrows under there it will release sulphur dioxide?"

thats what i was thinking at first- and is a little more of an issue!

would a tank full of worms and snails and only a SSB (plus accrued crap) get a chance for such a build up?

[clippo]

personally, I don't see what all the fuss is about with these systems. I've been running my tank without a closed loop for a couple of years now with average flow and have no detritus build up problems. Jas' post is interesting though - I think if your rock is placed on your sand bed, rather than sand being spread around the rock, you could have deadspots - otherwise, providing you have a pretty good reef structure, the only deadspots you get will be the same as those which occur in a upward flow reef structure. I also feel that using a reefrack etc, you lose the micro-habitats that occur where rock meets sand, such environments occur on a reef so why exclude them in our tanks?

[Tiggsy]

Originally posted by clippo@Dec 9 2005, 13:28
personally, I don't see what all the fuss is about with these systems. I've been running my tank without a closed loop for a couple of years now with average flow and have no detritus build up problems. Jas' post is interesting though - I think if your rock is placed on your sand bed, rather than sand being spread around the rock, you could have deadspots - otherwise, providing you have a pretty good reef structure, the only deadspots you get will be the same as those which occur in a upward flow reef structure. I also feel that using a reefrack etc, you lose the micro-habitats that occur where rock meets sand, such environments occur on a reef so why exclude them in our tanks?
that was my gut feel thinking as well but didnt have any experience to support it. considering the lareg sump/LR system i will have to deal with bio load i think i will leave the main tank as it is - a high flow upper area and a lower flow area under/behind it.

[zimreef]

Micro habitats obviously do occur where rock meets sand in a natural reef. However, no additional detritus occurs at this point in a natural reef as the water movement is such that no detritus ever settles. In theory then, the micro fauna that have evolved to live in this niche will not be able to do so in your tank as they're smothered in detritus.

Also water movement is just as important for those animals living behind the rockwork as those living on top of it so whilst I don't suggest for a minute that the underside of your rocks will be sterile, I think it will be healthier and support a greater biodiversity if there is a decent waterflow under and through the rocks too.

John

[Shinken]

Personally i think reefers are a over-worried lot! imho :thumbsup:

[clippo]

Personally i think reefers are a over-worried lot! imho

you're right there! :lol:

What I am trying to say is (not to hijack the thread or anything!) even if you have a closed loop system, you are bound to get pockets where there is low flow and a certain amount of detritus accumulates.. possibly even a lot!, it entirely depends on the flow pattern and shapes of the rock etc (and flow rate to some extent). Surely this is just as true for a tank without a rack (and a real reef for that matter) - you'll might get areas where detritus accumulates, and areas where it stays clear... but without a rack you don't lose the 'clean' micro-habitats. :wacko: :P

[zimreef]

Originally posted by Shinken@Dec 9 2005, 13:55
Personally i think reefers are a over-worried lot! imho :thumbsup:
:lol: :lol: :lol:

I agree with the sentiment entirely.

However, in most tanks we are trying to create as natural an environment as possible - in nature, these accumulations of detritus simply do not occur. If down the line Tiggsy encounters a problem where the cause proves hard to identify and says he has a large buildup of detritus behind the rock structure, the first thing that people will advise is to increase the water flow so the detritus doesn't accumulate.

Particularly when setting up a tank, given a choice between designing a system where detritus accumulates and designing a system where detritus doesn't accumulate - I know which design I'd favour.

In this case at least I think the paranoia may be justifiable ;)

John

[clippo]

still not convinced - I can think of several arguments against... but frankly I'm not that worried.

[simon garratt]

imo, the problems arise when people dont understand / or forget what type of environment they are trying to create and dont stock accordingly from the start. There is a marked difference between the typical/accepted habitats required for many LPS and soft corals etc compared to reef crest/slope SPS. On one hand a milder flow and mild detritus buildup wont cause too much concern, but the same cant be said for a dedicated reefcrest biotope where flow and low nutrient content is essential if you want to get near what nature offers and for your stock to grow anywhere near as it would in the wild. So to say it is something that reefers worry too much about is wrong imo as a blanket term. For some set-ups and stock, its crucial to success.

There is also the added factor that in cases where no3 accumulation is encounterd, its very common that a simple increase in circulation throughout the rock structure will lead to a rapid turn around in the overall health of the system including no3 levels to nearer our low target ranges, so it shouldnt just be an issue of detritus awarness. there is a very strong link between water chemistry (both system wide and by way of in-tank micro habitats) and the amount of flow present in any one area.

The crucial factor is allways to understand what your animals need and to desighn the system round what you want to keep. The 'dump it in and hope for the best' approach may work quite admirably if your only aspirations are a few mushies, a fungia and a few lagoonal LPS corals. Hell they'll probably enjoy it, but i very much doubt that youd get the same degree of success or longevity from trying the same thing with a predominantly SPS set up. not if you want to retain colouration, keep organics low and run anywhere near outer feef quality water.


YMMV :)


Si.

[SPS Hoover]

IMO its the most important factor in system design today.

[clippo]

so what exactly are the main benefits of this system then? seems to be suggested that its mainly reduction in nitrates, improved efficiency of rock?, if so, don't standard systems that run with very low nitrate levels suggest it isn't essential? - doesn't the increased technical complexity of such a system possess inherent drawbacks in itself?

[kim]

I'm not sure that it's more complex. But perhaps it takes more planning. A book of paper, pencil, ruler....

Eg you choose the tank size, then you envisage the rock formation that appeals to you....then you design the circulation to fit that plan (No idea ? Change that plan..)

Doesn't need to be closed loops involving lots of pipes or whatever. But a plan to get flow around that rock..

In the same way as people (hopefully) think about the amount of flow through their sump, and so fret about the pipe sizes and weir lengths which are needed to satisfy that flow, perhaps they should also see their LR as a filter, which also needs a certain flow, and think about what would satisfy that. Then also their stocking.....what (when it has grown) could impede or be damaged by that flow ?

Sure, the best laid plans fall apart, ideas on stocking change, and everyone makes mistakes that in hindsight are so, well, crap. :blush:

Hopefully, a powerhead or two will compensate. But if people plan a little, and at the very outset imagine how they would like the tank to develop (in their dreams) they probably have a better chance of getting there. Good planning hopefully allows for a bit of flexibility. Oversize the pipes, plan for access...

It's painful - there are so many ways to cut the cake......which one ? For indecisive control-freaks like me it's a total nightmare.

But it's not rocket science.

kim

[Shinken]

So to say it is something that reefers worry too much about is wrong imo as a blanket term

I wasnt saying they should ignore it. Worrying dosnt help things doing something about it does :thumbsup: