# Necessary flow through filter



## jameson_uk (6 Mar 2018)

I was just thinking about what level of flow you actually need through an external filter.  I know you need flow to distribute nutrients but this could be achieved with a powerhead.  This is purely out if interest as I was wondering why more people don't just do something like use a small powerhead to drive a spray bar and drop to a less powerful filter?

My eheim 2217 has a capacity of 6l and I know that nitrification needs oxygen so if flow drops it could get anaerobic which would be bad but if you treat flow around the tank as a separate issue then I am guessing you don't need 1,000 lph to achieve filtration?

Assuming that the water is reasonably well oxygenated then would a lower flow rate actually cause issues?  I am assuming the driving factor would be turnover so it would depend on tank and filter size but what rate of turnover is necessary?


----------



## AverageWhiteBloke (6 Mar 2018)

I don't think it would actually matter how you achieve good circulation as long as you do. I would imagine the reasoning behind the 10x rule would be sufficient flow created by something that is outside of the tank and not spoiling the view.


----------



## ian_m (6 Mar 2018)

AverageWhiteBloke said:


> I would imagine the reasoning behind the 10x rule


The x10 rule was to allow for rather optimistic manufacturer filter ratings & when used with actual real world filter media. 

My JBLe1501, you would think having 1500 in the name would mean 1500 litres/hour, but no the pump is rated 1400 litres/hour. However, digging around in the instructions reveals a filter rate of only 800-900 litres/hour when used with 1.5m hose and clean filter material. So real world with dirty filters will be much less. Some "cheaper" filters are often a lot worse the real flow being as little as 1/4-1/8  the rate quoted rate on the box, even when clean.

So I would try to aim for x10 filter turnover and suppliment with power heads as necessary.

This is of course assuming you are EI dosing, spot on CO2 and monsterous lighting. If lighting is much less than flow & turnover is not so important.


----------



## jameson_uk (6 Mar 2018)

I guess what I was looking for was how low flow can you get away with in a filter and still have it do its job assuming flow was dealt with elsewhere.  If I had say a 1,000 lph powerhead plugged straight into a spray bar I would get the same flow as the filter (assuming they are also optimistic on flow rate) but what level of flow would be needed through the filter to keep it aerobic and provide mechanical, possibly chemical (and some biological) filtration ???


----------



## a1Matt (6 Mar 2018)

Interesting question. I don't know know but would hazard a guess, that very little flow is needed in the filter.

Sponge filters provide biological filtration with the absolute bare minimum of flow.

I think the important point, as you say, is that the water flowing over the media has to contain sufficient oxygen for the bacteria to utilise. (Otherwise you end up with anaerobic conditions in the filter.)

Maybe as there is more media in a canister it needs a bit more flow than a sponge filter so that the oxygen isn't 'used up' before the water finishes it's journey out of the filter.

I'd guess 1x is plenty.

With this logic, your powerhead on a spraybar seems like a really good combination with a low flow filter.

If there was a shrimp safe version, I'd contemplate a wavemaker + hob/tiny canister combo.


----------



## doylecolmdoyle (6 Mar 2018)

Sometimes I think people "talk up" flow, is it really that critical? on my 60p tank (17g) I only use a filter rated for 360/lph and I am sure it flows way less than that... the tank does fine, I also use the same filter on another 2ft tank that is stuffed to the brim with java fern and again that tank is doing well. I guess both tanks only have fairly easy to grow plants but both do well with just a cheap small canister filter. You can sell the little Ista External Mini Canister Filter (360lph) sitting next to the 2ft tank.


IMG_1192 by Colm Doyle, on Flickr


----------



## dw1305 (6 Mar 2018)

Hi all, 





jameson_uk said:


> My eheim 2217 has a capacity of 6l and I know that nitrification needs oxygen so if flow drops it could get anaerobic which would be bad but if you treat flow around the tank as a separate issue then I am guessing you don't need 1,000 lph to achieve filtration?


Yes, you really need to treat biological filtration and flow as separate issues. 

If you could ensure that all the media was oxygenated, an Eheim 2217 contains enough biological media to treat a huge bioload.  An additional power-head would provide the flow you need. 

The actual volume of filter media is very rarely an issue in biological filtration, people often don't realize this and buy bigger and bigger filters, but without doing anything about the oxygen supply.  

When you tell people this they often talk about "dwell time" and "pore space" and link to the promotional material from vendors of special porous filter, but it is all smoke and mirrors. 

Have a look at <"What filter media is best....">.

cheers Darrel


----------



## Gill (6 Mar 2018)

I use a 1200lph jebao external with  spray bar, In the Canister from bottom up -  Alfagrog, Biohome sticks, Bio Beads, Course, Fine, Floss. Large Sponge Filter (fine) as prefilter. 
+ 1200lph jebao internal Course and Fine. Both turned to full


----------



## Gill (6 Mar 2018)

I Also Have a Baki type Trickle Shower_(3 Level,12 Trays)_ that fits on top of the EA600. Which gave amazing filtration, and had Hydrocotyle planted in the baskets. Not used it this time round though.


----------



## Majsa (6 Mar 2018)

What do you mean by plugging the powerhead straight into a spray bar? I find this interesting, also considering supplementing my 1050l/h canister filter with a powerhead in a 175l tank.


----------



## jameson_uk (6 Mar 2018)

Majsa said:


> What do you mean by plugging the powerhead straight into a spray bar? I find this interesting, also considering supplementing my 1050l/h canister filter with a powerhead in a 175l tank.


A lot of powerheads connect to pipework so I was thinking you could connect the pipework direct to a spray bar.

http://www.eheim-aquarium-parts.co....installation-set-2-nozzle-adapter-set-4009700
Should allow a hose to be connected to the eheim spray bar


----------



## ceg4048 (7 Mar 2018)

jameson_uk said:


> I was just thinking about what level of flow you actually need through an external filter. I know you need flow to distribute nutrients but this could be achieved with a powerhead. This is purely out if interest as I was wondering why more people don't just do something like use a small powerhead to drive a spray bar and drop to a less powerful filter?


Because strapping a rocket nozzle to the back of the tank is ugly. The idea of a planted tank is to create the illusion of a natural stream or pond and to remove, as much as possible, all visual cues of hardware from the tank which ruin the illusion.
Naturally, the first priority, as you mentioned, is to ensure the health of the plants, so if the filter being used is weak then the flow and distribution need to be augmented. It's a lot cheaper to buy a powerhead than it is to invest in a replacement filter with a more powerful throughput however.



jameson_uk said:


> My eheim 2217 has a capacity of 6l and I know that nitrification needs oxygen so if flow drops it could get anaerobic which would be bad but if you treat flow around the tank as a separate issue then I am guessing you don't need 1,000 lph to achieve filtration?


You might be missing the point here (or I may be misunderstanding your point) but you do not need 6L of filter media in a planted tank. The plants do the work and they bypass nitrification. In so doing they oxygenate the water better than any filter could dream of doing. Of course this assume the plants are healthy and that there is sufficient plant mass. Adding 6L of filter media will actually choke the flow and in so doing deprive the plants of receiving the nutrients and CO2 necessary for them to perform efficient oxygenation. From an aesthetic viewpoint, many people make the mistake of adding a powerhead to improve flow/distribution when they might have been able to make the improvement by removing all that filter media, especially those absurd noodles and ceramic balls.

In a fish only tank the element of the plants is missing so oxygenation has to be achieved via air bubbles and so forth. 

In both cases however, frequent and large water changes help to remove organic material which will reduce the removal of oxygen by bacteria. CO2 fed plants produce a LOT of organic waste and so tank cleaning is imperative.



jameson_uk said:


> Assuming that the water is reasonably well oxygenated then would a lower flow rate actually cause issues? I am assuming the driving factor would be turnover so it would depend on tank and filter size but what rate of turnover is necessary?


But this is a big assumption that a tank is well oxygenated. Just exactly how is this supposed to happen. In aquariums, the commodity that is always in the least supply is oxygen. As I indicated above, the way that you _achieve  _"well oxygenated" water is to have sufficient flow/distribution in order to deliver the necessary raw materials to the plants for them to oxygenate the water.



doylecolmdoyle said:


> Sometimes I think people "talk up" flow, is it really that critical?


Yes, I'm one of those who talk up flow all the time, and that's because I know and see that improved flow fixes a LOT more problems than does low flow. Sometimes, in a tank that is suffering poor CO2 or poor nutrition, the hobbyist can resolve the issues by simply removing filter media, or by simply rearranging the filter outlets. 

Again, there are quite a few variables, such as plant variety, tank size, lighting and so forth as you noted, but every tank and every hobbyists is different and in order to solve some basic problems, attention needs to be paid to flow/distribution. So the 10X rule is just a basic guideline to help keep folks out of trouble. Does this mean that there are no exceptions or that variations are not possible? No but compare that advice to the traditional advice offered by the "add more light" camp, and you'll see that many more problems are fixed by attention to flow than attention to increased light.

I've noticed that a lot of advice being given by experienced hobbyist to beginners never take into account that the beginner really has no idea why a concept works or does not work, or how a deviation from a standard procedure can be used successfully. The person offering the advice subconsciously assumes that the beginner knows what he know or understands what he understands. I always assume the opposite because I know that many people are coming from a fish-only culture infected with all kinds of  fears and misconceptions, so I always try to guide them towards the rules of thumb that we have seen in our experience that avoid common trouble. As the person gains experience we can see that they easily deviate from the basic advice to experiment or for convenience, but they can do so successfully because of being armed with a better understanding of cause and effect.



jameson_uk said:


> A lot of powerheads connect to pipework so I was thinking you could connect the pipework direct to a spray bar.


If you're going to use a powerhead then just use it the way it is and get on with it. As long as it's mounted properly, i.e. central and just below or just above the spraybar pointing in the same direction then it will be fine. Attempting to connect it to other components usually results in loss of efficiency or reduction of flow rate.

Cheers,


----------



## jameson_uk (7 Mar 2018)

ceg4048 said:


> Because strapping a rocket nozzle to the back of the tank is ugly. The idea of a planted tank is to create the illusion of a natural stream or pond and to remove, as much as possible, all visual cues of hardware from the tank which ruin the illusion.


I started off with a tank that had plants rather then an aquascape.  I think a lot of people probably do this as they go to LFS, get a tank, buy some plants where as here the emphasis is far more on aquascaping.  The spray bar is there already and the powerheads are tiny, my tank has a big ugly hood which hides quite a lot (unfortunately I don't have one of the nice rimless, braceless ones) so adding a powerhead to the existing spraybar would not really be much more visible that what is there already (and a couple of tall plants would hide it too).



> You might be missing the point here (or I may be misunderstanding your point) but you do not need 6L of filter media in a planted tank. The plants do the work and they bypass nitrification. In so doing they oxygenate the water better than any filter could dream of doing. Of course this assume the plants are healthy and that there is sufficient plant mass. Adding 6L of filter media will actually choke the flow and in so doing deprive the plants of receiving the nutrients and CO2 necessary for them to perform efficient oxygenation. From an aesthetic viewpoint, many people make the mistake of adding a powerhead to improve flow/distribution when they might have been able to make the improvement by removing all that filter media, especially those absurd noodles and ceramic balls.





> But this is a big assumption that a tank is well oxygenated. Just exactly how is this supposed to happen. In aquariums, the commodity that is always in the least supply is oxygen. As I indicated above, the way that you _achieve  _"well oxygenated" water is to have sufficient flow/distribution in order to deliver the necessary raw materials to the plants for them to oxygenate the water.





> If you're going to use a powerhead then just use it the way it is and get on with it. As long as it's mounted properly, i.e. central and just below or just above the spraybar pointing in the same direction then it will be fine. Attempting to connect it to other components usually results in loss of efficiency or reduction of flow rate.


As above, I started out as a fish tank and added plants.   I therefore started out with the _suggested _media for my filter but I have cut this down and 6L capacity isn't filled with media.  
Assuming you have sufficient flow/distribution generated by a powerhead and decent surface agitation (I run low tech so no big issues with CO2 gassing off) then you will get the oxygenation regardless of the filter.

I guess the point of my original question (which was theoretical more than anything) was if a powerhead was taking care of flow / distribution in the tank then what flow is actually necessary through an external filter.  Is there some sort of turnover which is necessary to perform adequate mechanical filtration? When could the filter become anaerobic (I guess even if you only had a couple of sponges in your filter there would be biological filtration going on and if you had really low flow this could easily turn anaerobic)?

I hadn't really seen anyone implementing this type of system where they ran a powerhead to handle flow alongside a smaller / less powerful filter and wondered why more people don't do this (aesthetics aside).


----------



## doylecolmdoyle (8 Mar 2018)

ceg4048 said:


> Yes, I'm one of those who talk up flow all the time, and that's because I know and see that improved flow fixes a LOT more problems than does low flow. Sometimes, in a tank that is suffering poor CO2 or poor nutrition, the hobbyist can resolve the issues by simply removing filter media, or by simply rearranging the filter outlets.
> 
> Again, there are quite a few variables, such as plant variety, tank size, lighting and so forth as you noted, but every tank and every hobbyists is different and in order to solve some basic problems, attention needs to be paid to flow/distribution. So the 10X rule is just a basic guideline to help keep folks out of trouble. Does this mean that there are no exceptions or that variations are not possible? No but compare that advice to the traditional advice offered by the "add more light" camp, and you'll see that many more problems are fixed by attention to flow than attention to increased light.



Very true, I do agree flow is a key element in establishing a balanced planted tank, as you said variables will effect just how much flow you need. Now I did say I have 2 tanks that probably have only around 2x turn over and do fine, but I did have a 3ft tank that really suffered until I upgraded the filter to provide about 10x turn over, again every setup is different! I agree aim for 10x flow and generally less light


----------



## dw1305 (8 Mar 2018)

Hi all,





jameson_uk said:


> When could the filter become anaerobic (I guess even if you only had a couple of sponges in your filter there would be biological filtration going on and if you had really low flow this could easily turn anaerobic)?


Yes, so potentially if you had enough dwell time and some bioload, eventually all that oxygen will be used.

The rate of oxygen use would depend upon the Biochemical Oxygen Demand (BOD) of the water. If you had a liquid with a very large BOD (say milk) it would be impossible to use a sealed container (like a canister filter) for aerobic nitrification because you couldn't pump the milk through quick enough to keep the oxygen replenished.

Unfortunately we are into <"Donald Rumsfeld territory"> here, and there are too many parameters we can't measure to get a definitive answer.

You can get robust oxygen probes for fermentation monitoring, that would work if you adapted your canister (basically drilled a hole in the filter body and added a seal-able port), but <"they aren't cheap">, and you also need a <"dissolved oxygen meter"> to connect them to. Because we can't measure dissolved oxygen levels we need to use <"proxies to estimate oxygen levels">.

If you have a look at <"Plecoplanet: Aeration and dissolved oxygen...">, it covers a lot of the relevant areas in some detail.

What we are really interested in is the range of oxygen values, and particularly what the lowest values are, and how long they occur for. Canister filters are different from other areas where biological filtration occurs (the substrate, HMFs, HOBs etc.) because they are sealed containers where a finite amount of oxygen enters and this can't be replenished until (the water containing) it leaves the canister.

In a planted tank you only have to worry about low oxygen levels at night, but in a tank without plants it is always "night". 





jameson_uk said:


> I guess the point of my original question (which was theoretical more than anything) was if a powerhead was taking care of flow / distribution in the tank then what flow is actually necessary through an external filter. Is there some sort of turnover which is necessary to perform adequate mechanical filtration?


This going to depend on the tank architecture. You would need to balance the flow with the coarseness of the filter media. If you have a fine media and high flow you are going to get media bypass pretty quickly.  Personally I like to try and keep all the mechanical filtration outside of the filter body, either in the pre-filter or by having a low flow area in the tank where I can syphon debris from.

cheers Darrel


----------

