Water flow in the planted aquarium?

Discussion in 'Filters, Filtration and Pumps' started by Steve Smith, 18 Mar 2008.

  1. Steve Smith

    Steve Smith Member

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    Hey all. I've noticed that over filtering, and good flow of water around a planted aquarium seems to be mentioned a bit in some of the posts I've been reading of late. I just wondered what is best. Is it just high water turn over, or is it specifically good flow around stems/substrate level that helps?

    Whats the basic science behind it?

    On that note, I am due to setup a second external filter, doubling the turnover of water in my 180 litre tank. I wondered what positioning works best? Opposite ends, same ends, spray bars/single outlet?

    Thanks in advance :)

    Steve.
     
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  2. Ed Seeley

    Ed Seeley Member

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    Well I think a general consensus here seems to be to aim for about 10 times the tank volume per hour, but higher seems better than lower if in doubt as filters never run at their stated flow rates. The idea is that high flows ensure CO2 especially, but all other nutrients too, are quickly and evenly distributed around the tank. It also helps to ensure that detritus is kept in suspension longer and swept into filters keeping that potential source of organics away from the tank where it could trigger algae. Higher flow rates also usually go hand in hand with more filter media too, again reducing mini-ammonia spikes.

    As to the form of that flow I don't personally think it matters too much, but it must be flowing all around the tank to ensure no plants go without and detritus doesn't collect. Some use spray bars, some lily pipes and I have a Hydor flow pump to boost circulation. Personally I like this method as I already have sufficient, high surface area media (Sintered glass) IMO in my filter and I can then turn the pump off at night when the CO2 is off and give the fish a rest. After all the fish I am keeping aren't from rapids! Or even quickly flowing streams.
     
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  3. ceg4048

    ceg4048 Expert/Global Moderator Staff Member

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    Hi,
    I agree with Ed. There are two issues. Nutrient delivery and High surface are media for bacterial colonies. Check page 6 of this thread for some gory details: viewtopic.php?f=35&t=1011&start=50

    Cheers,
     
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  4. Steve Smith

    Steve Smith Member

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    An interesting read indeed. I'm now considering the sintered glass media, though I bought a large bag of bio balls last night, so might stick with those. I think I am going to fill one half of the new filter (Fluval 204) with the bio balls, increasing my bio filtering quite a lot. The other half is designed to take mechanical sponges so I'll stick with those. I think I'll also increase the bio filtering in my current filter.

    As for positioning of the outlets, I think I'm going to switch to using a single outlet instead of spray bars, and position them to give reasonable flow in slightly differing directions, and possibly slightly differing heights if possible, towards the two inlets on the opposite side of the tank, also at different heights.

    Thanks for the info guys :)
     
  5. Lisa_Perry75

    Lisa_Perry75 Member

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    Just sent it today :D I protected it with bubble wrap and a sheet of filter floss as you didn't have any media. Cost £8.25 to post it! 2.7kg hehe.
     
  6. Rob33

    Rob33 Member

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    How about having a spray bar mounted vertically? Anyone tried this?
     
  7. Ed Seeley

    Ed Seeley Member

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    I don't know but the problem I see with spray bars (though I know Clive uses them) is to think about a water spray you use on a hose pipe. I have one with nozzles that can be changed. When I use the rose (my spray bar analogy with lots of small hoses) the flow feels less intense whereas when is use the single soaker attachment it pushes things around. I see the same kind of effect in my tanks, so I like to use the open end return rather than a spray bar. Please note this is an advantage, I feel, in mainly keeping debris suspended; I'm not sure it will make a difference to CO2 or nutrient distribution.

    Clive had tried out a number of different ways of mounting spray bars for best effect I think.
     
  8. Rob33

    Rob33 Member

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    Yes, I see your point.
     
  9. ceg4048

    ceg4048 Expert/Global Moderator Staff Member

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    Hi,
    Smaller tanks can use a variety of ways to move the water since the distances are not very large and so there's less loss of momentum. The larger the tank the more difficult it is to keep from getting stagnant areas, especially if the tank is tall. The flow simply peters out and cannot carry CO2/nutrients to the deeper recesses of the tank. In such tanks you get areas that have excellent flow and the plants in those areas do well. Other areas suffer starvation and the plants mysteriously disintegrate or just do poorly. This is particularly true for carpet plants which have the worst of all worlds:
    1. They are closest to where decaying detritus settles and where pockets of ammonia develop, with a greater likelihood of producing algae due to a higher ammonia loading rate.
    2. Flow rate is lowest here and CO2 tends to rise away from them.

    In deep tanks therefore the idea is to force flow downwards against the front glass to ensure maximum contact time. When combined with an external inline diffuser, CO2 enriched effluent is poured down over the carpet plants if the spray bar is mounted against the back wall. Since you want maximum coverage along the length of the tank, mounting the spray bars vertically is counterproductive since this causes a narrow sliver of flow. I've found that if the carpet plants are fed in this manner all the rest of the plants are automatically fed as the the flow is deflected towards the rear and then up along the aft wall. This method allow the water to penetrate even to the floor of the back wall.

    In many tanks, tall growing stems have a tendency to lose their lower leaves and it has been assumed that the reason for this is that these lower leaves have less light. I'm beginning to believe that this is only partially true as many of my plants don't lose the lower leaves at all. If these leaves have sufficient contact time with CO2 laden water they can still photosynthesize as would low light plants. Many of my plants retain their lower leaves, even in the shadows. The key, I believe is due to better CO2 and nutrient distribution facilitated by the hydrodynamics of properly mounted spraybars.

    The first image below shows the lower half of a 12 inch stem. Peering deep into the shadow area you can see that that this "so-called" high light plant (P. Stelleta) still retains the lower leaves. There is even pearling on the lower side of the leaf surface as the CO2 laden water flows in an upward direction. I never saw this behavior when using lily type pipes, which only send strong flow longitudinally. The second image shows the upper half of this plant (left side of that frame). Compare the relative levels of light from left-top to left-bottom of the frame (note that the first image looks bright only because of the camera's exposure settings.) You can see that although the lower leaves are smaller they do grow and do not shed. In fact, all along the bottom of that image you can see the amount of shading but these plants have no difficulty growing. I attribute this in large part to the spraybar configuration. Again, note that I'm only talking about large tanks. Ed's analysis is for smaller volumes.
    8394061315_e46e62cba4_c.jpg

    8394064529_72a2703d5f_c.jpg

    In this shot you can see C. wendetii on the right which I prune often, except I pull the lower leaves. The lower leaves on this plant grow out from the shadow area smothering the carpet plants. You can just make out on the bottom of the frame that the P. helferi has little difficult propagating even into the darker areas. Force feeding CO2 via the bars makes this all possible. Now if I could only find some spray bars that do not have EHEIM written all over them. :(
    8394087377_9568024388_c.jpg

    Cheers,
     
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  10. Steve Smith

    Steve Smith Member

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    Wow, great info Ceg :) So do you have just one spray bar, or 2? Would be interested to see how it looks.

    I guess one of the issues might be if I were to rig up an inline reactor (as I hope to do) the CO2 would only be comming from one spray bar. Do you mount it as close to the middle as possible?
     
  11. ceg4048

    ceg4048 Expert/Global Moderator Staff Member

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    Hi Steve,
    Here is a photo of a sample installation. You might just be able to make out the back glass. There are actually 3 spraybars. Two of them are ganged together on the left side with an inch long piece of tubing. I was too cheap to buy a 4th for the right side. Remember this is a 6 footer. This is not a very sophisticated installation at all. They are just mounted on the back with suckers and just joined to the filter outlet tube. I don't even use the shepherds crook, no need and better flexibility. Now, Fred Flintstone and Barney Rubble would have done it this way so I'm not particularly proud of it's lack of modern aesthetic appeal but it works. The holes in the bars point straight out - horizontal towards the front, maybe even slightly upwards. I previously had HC in the foreground which used to just decay when I used the £40 lily pipes. Subsequently, after spraybar installation, huge mats of it would detach from the substrate due to the buoyancy from pearling, which actually became annoying.
    8396954239_ff17a4e4ab_c.jpg

    This shot shows the bars more closely and shows the orientation of the holes. I found a much better behaved ground cover plant (P. helferi) and it also benefits from this simple configuration.
    8396953793_920569535d_c.jpg

    I use two inline diffusers and two filters, one is a Cal Aqua and the other an AM1000. Ideally, mount the spraybar centrally but you can do as I did and join two bars together. This gives you better coverage and lowers the exit velocity at each hole because there are more holes. On my setup there are a few gaps, like at the two far ends of course and a foot or so in the middle. No big deal.

    Remember, if they look too ugly you can mount them way up at the waterline so that you hardly notice them. Of course, real aquascapers would never even consider such a cheesy setup, but hey, it works. Just you try growing a 6 foot mat of HC 2 feet underwater. Not even remotely easy. :wideyed: This give you the best chance. Anyway, I've completed a self hypnosis course and now I tell myself "what spraybars?" :p

    Cheers,
     
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  12. SuperColey1

    SuperColey1 Member

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    P@H sell plain transparent Fluval spray bars for external and internal filters. no branding on them.

    Andy
     
  13. ceg4048

    ceg4048 Expert/Global Moderator Staff Member

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    Great tip Andy! Thanks for that. I'm off to P@H!

    Cheers,
     
  14. beeky

    beeky Member

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    Do B&Q and the like sell 12mm and 16mm tubing for general purpose plumbing use? Eheim and Fluval seem to charge an awful lot for bits of plastic tube.
     
  15. ulster exile

    ulster exile Member

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    Eheim do grey "installation sets" which aren't branded and in my humble opinion look more stylish than the green. Charterhouse aquatics (online) stock them afaik.

    I have a 2026 (c950 lph flowrate) on my 215Litre(ish) tank with the spraybar extended to nearly half of the tank's width. I have positioned the CO2 diffuser under the spraybar and I do see a nice stream of bubbles rising from the diffuser, reaching to near the surface and then being pushed back down and to the front of the tank in a circular motion.

    My only concern is that currently the bulk of my plant mass is on the side on which the diffuser/spraybar sits so the bulk of the plants are well served (imo!), but the other side of the tank isn't as well served by this arrangement. Would it be better to extend the spraybar further and accept a reduced flow from the spraybar overall or leave as it is, do you think ,as I will probably end up putting in more plants on the less well served side?
     
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  16. ceg4048

    ceg4048 Expert/Global Moderator Staff Member

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    Hi Chrisi,
    Just to be clear, the flow rate does not change by adding an additional bar. The exit velocity at each hole decreases but there are more holes so that the total flow rate is held more or less constant. I have seen a better overall distribution by extending the bars across the entire width. This same circular flow you describe will occur along the long axis of the tank so I reckon that's a good thing. There are a couple of issues to consider though which may either improve or curtail the effectiveness.

    Strong velocity from only a single bar does help to push the CO2 down the front. The higher kinetic energy of the effluent improves contact time of this water in the deeper region. You may notice that the tiny CO2 bubbles are like salmon swimming upstream as they rise. The longer they are submerged the better. Once you extend the spraybars effective length and thus lower the exit velocity from each hole though, there is a lower kinetic energy so contact time at lower depths may be less. The bubbles may rise and escape faster.

    A single diffuser on larger tanks will always result in an uneven distribution so you would have to experiment to find the best placement. Two diffusers would be better. Still better would be to switch to an external diffuser. That way the entire length of spraybar is filled with CO2 laden water and the distribution is more even at each of the the exit holes. The little Cal Aqua glass inline diffuser, although obnoxiously expensive, does a really good job in my opinion. A combination of the Cal Aqua and an extra spray bar would give pretty good coverage. If you don't want to go the external route then perhaps just tweaking the injection rate bit more would be the next best thing.

    I did finally get rid of the Eheim bars in favor of two sets of Fluval smoke gray bars. A mere 10 quid for 2 feet worth of plastic, so I was really grinding my teeth (I figure it cost Fluval 2 pence to manufacture each kit :twisted: ). The diameter is slightly larger than the Eheim bar so it's a bit of a struggle to get the Eheim 16/22 hose over it. A little bit of hot water on the hose does the trick. They look a lot better as they tend to disappear in the background. I'm quite satisfied with that (the Gucci glassware fraternity will be rolling their eyes in disdain about now I imagine :p )

    Also remember that although your 2026 is rated at 950lph, if it's filled with media and is 2 feet or more below the water line then it's probably delivering only about 500lph or so in real terms.


    Beeky, you could probably get the bars from the DIY shops. You'd have to drill your own holes though.

    Cheers,
     
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  17. beeky

    beeky Member

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  18. Steve Smith

    Steve Smith Member

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    Great info guys :)

    I'm currently using the tetratec spraybar on my EX700 and the grey Eheim kit on my Fluval 204. Managed to find them at my LFS for £10 for the spraybar, £10 for the intake. While still expensive thats saving about £10 on RRP for both!

    I want to get an external reactor but don't think I can afford 2. 1 will be stretching it! I really want to move away from internal ceramic diffusers.
     
  19. Ed Seeley

    Ed Seeley Member

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    DIY it! It's not as hard as you might think! I've built one using a gravel cleaner and a few plastic media balls and it worked great or you can use PVC pipe.
     
  20. Steve Smith

    Steve Smith Member

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    Its the hose tails that worry me. I've seen some guides but not really sure if I can get the parts. I should have a browse around B&Q at the weekend.

    Any chance of some pics of your DIY effort? (might be worth a seperate thread).

    Cheers

    Steve.
     

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