Filtration rates, flow, and other questions

Yes, Ashley, Shibby and freerider,

In essence, the less media, the higher the flow rate would have to be. However, there is a cut-off at which the low media, high flow rate is just simply not going to cope and this will then lead to increase nitrite levels with consequent negative effects particularly when keeping discus. A filter with limited medium obviously is also more prone to becoming blocked and therefore has to be monitored very closely so that this does not happen.

In general, therefore, filters with a bigger volume of medium are better. I could add some very complex chemical arguments with regard to redox potential to this discussion, but in order to keep it simple, it can be said that the deductions that we have made are correct and are a good guideline. In discus keeping or if you keep altums biological filtration (as we have discussed now) and biological load (the number of fishes in an aquarium) needs to be balanced very carefully in order not to cause an overburdening of the system which leads to a lower redox value and which in turn is negative for the fishes.

Kind regards,

Dirk

 

Hi all

I would like to contribute a small piece of information here. In some articles written by the people from ADA (Takashi Amano's company) they often refer to filter capacity in terms of volume, and they recommend 10% of the tank capacity. So for a 300l tank they propose you install a 30l filter. I have a TetraTec EX1200 on my 300l tank and the filter's capacity is 12l. The flow rate is, of course 1200l/h, which is 4x my tank volume. So what these guys are saying is that I need more than double what I have right now. The TetraTec is filled with Sera Siporax, which I believe is the best biological media. I suppose I can also back down the flow rate out of the filters, should I decide to buy another and install it.

 

Hi All
I just went through this thread and still not the wiser
If I understand al this correctly
The bigger the filter volume the better! 2 reasons increase overall water volume and theoretically increased media surface
Flow rate about 1-5 times tank volume: to high a flow rate not enough time for nitrobactor to do there job to low flow rate not enough mecanical filtration and insuficient nutriens (Oxygen, NO4 etc) to keep a stable bacteria density.
Mixed filter substrates (mechanical fine filter, porous solid biofilter)
If at all possible a anerobic section to remove nitrate's.
If I get this all right than the near ideal filter setup would be for a 4ft 250L tank a sump filter with a capacity of lets say 50l and 4 chambers.
1st chamber "filter wool" second chamber: ceremic tubes lava gravel etc. third chamber: deep sand bed. fourth chamber clearwater for pumb (+/- 300-1000L/h) heater etc?????

 

Hi Guido,

Some of the things that you have deduced are correct, others I can make some more suggestions about.

You are correct that the bigger the volume, the better. Water volume increase (I assume you mean aquarium and filter water volume) is actually not important, but increase media surface is what it is all about, quite correct.

The next point that you make is largely also correct, but it is ammonia and nitrite that are nutrients of the bacteria and nitrate is the product of the bacteria. In order to perform this process oxygen is vital, absolutely essential and if there is too oxygen then the biological filtration will also be limited by oxygen shortage.

Mixed filter substrates is also correct.

An anaerobic section is a luxury and you need to specifically work at getting an anaerobic filter to work, so for most filters this type of filtration does not apply. You can also reduce nitrate amounts by water changes so an anaerobic filter is not essential.

Your near ideal sump with four compartment is where you are going wrong. Four compartments means that the water flow is constricted four times, this will reduce flow rates and the filteration rate that can you achieve will simply be too low. What you need is a single compartment with the media in layers, then you can in total have a much better flow rate over this. This is quite difficult to grasp, and whilst I thought I could get away without showing you some sump designs, I think I must make some sketches, scan them in and show them to you, so that I can explain this better.

Kind regards,

Dirk

 

One thing i dont uderstand is how a sump with more compartments can reduce flow rates ? Isnt the flow rate through the system determined by the return pump`s output ? For instance, if you have a 3000lph return pump (lets ignore head loss for the example) there will be 3000 liters of water moving through the sump each hour, if the compartments reduced flow the return chamber would run dry pretty soon and the compartment(s) would flood ? The only thing adding more compartments will do is speed up the the flow of the water through the media as the 3000 liters of water now have a longer path to travel, which could mean less contact time with the filter media. I also think total water volume is important, a large body of water is more stable with regards to ph (and other parameters). That is why a big tank is often easier to keep than a nano and why i would use a 4ft sump with a 4ft tank for almost double the water volume.

 

Although this may not appear logical less larger compartments versus more smaller ones is precisely the important thing that you must understand. More compartments means that the bore of the filter is reduced. Let is say that you have 4 compartments following each other of which the measurements are 20 x 20 x 20 cm each. The flow is decided by the surface area of one compartment in other words 20 x 20 cms = 400 cm2. If this compartment slows down the flow of the water, the total flow will be reduced and every compartment will slow down the flow again and again. Let us say that instead of 4 compartments you now only have one of which the dimensions is that of each of the compartments, in other 80 x 20 x 20 cm. If you calculate the surface area then you get 80 x 20 cm = 1600 cm2 in other words 4 times the total surface area. Now this will therefore not restrict the flow so much because of the much larger surface area. Let us say that you wanted to pump 200 litres per hour through this filter, then in the 4 compartment filter the water has to flow through 20 x 20 = 400 cm2, whilst if you have only one compartment of 80 x 20 = 1600 cm2 then your flow rate through this filter of 200 litres has a much larger surface that the water has to flow over. This means that it is not going to clog up as fast and it also means that due to the fact that the water flows over the medium more slowly, the bacteria can do their job better and your biological filtration actually improves.

I have visited many major discus keepers in Germany over the years and this is exactly what I saw again and again and I use it throughout my systems and it works much better than smaller compartments which clog up. I always say, reduce the number of ups and downs but keep the same filter volume and your filter will work much more effectively, both in terms of mechanical and biological filtration.

Kind regards,

Dirk

 

Dear Professor
I do not want to question you or your expertize but one thing is still not clear to me
Your example above the 20x20 i dont understand
Lets say I have a 25mm inlet pipe. This pipe gives me a 4.9sqcm flow space. If , and I still refer to a practical setup for a 4foot tank, my sump, and I like to place them behind the tank, is 120 x 45 x 10 cm than my sump would give me 54L
If my flow channels are 1sm by 10cm than I have a flow area of 10sqcm
Never mind what amount of water I wanna pump thru my filter it has to come thru the inlet.
The "Bore" of the filter is at least 2x bigger than the bore of the inlet.
I only start to reduce the flow rate if I put filter material into the set-up ??
And the smaller the individual units are the easier is the cleaning without disturbing the rest of the sump setup??
I tried to scetch what I mean in the drawing but please excuse my limited success (-:

 

Hi Guido,

I am not questioning the inflow, I am accepting that the inflow is always larger than the flow through the filter. As you quite correctly indicate, you reduce the flow rate if you put filter material into the set-up. So, when you 10 sqcm is blocked, that is it, the flow will slow down. If you have one filter chamber that is much larger, then it will take longer to get blocked and therefore you will not get blockage problems as quickly. What is however an additional problem is that every chamber will reduce the oxygen content and if you keep the filter area larger this is less.

Cleaning of these smaller sections may appear easier because they are smaller, but the reduced flow is far worse than disturbing the filter medium. You can also just remove the top sponge of filter wool layer of a large filter and not touch the rest, and you will not cause any disturbances.

I hope you can understand, although this may not appear to be so easy, it does have major advantages and is so crucial that this is the make or break of a good filter.

Kind regards,

Dirk

 

I suppose here we are all going to be "flabberghasted"... the theory says one thing, but the practice says another. (Something I think we have all experienced??)

I have actually seen a few Marine Sump set ups with only 2 chambers... and I know these guys are fussy... so there must be something to this less chamber thing. Prof, i would be very interested in seeing your sketches on how you suggest a sump design??

 

Hi Ashley and Guido,

I do not know why you are battling to understand the concept here. Let me try a different explanation. Let me get back to my example of 4 chambers of 20 x 20 x 20 versus one chamber of 20 x 80 x 20. If you take the four chamber setup, you are allowing the water to flow over one 20 x 20 x 20 chamber then you have a up down and then the next 20 x 20 x 20 cm and so on. Effectively, this is as though you would have all four of the 20 x 20 x 20 cm units stocked on top of one another, in other words really 20 x 20 x 80 cms. This means in such a filter the water would have to flow through 80 cms of medium and the bore of the filter would be 20 x 20 cm. The filter would clog up far faster because its area is only 20 x 20 cm, top layer would take all the oxygen and the rest of filter of the filter would not work properly because it needs oxygen to do the ammonia to nitrate conversion.

Now if you look at the single cell filter of 20 x 80 x 20 cm (last measurement depth), then the surface area of the filter is much greater and will get clogged less quickly, the flow rate less restricted and because the water flow is slower you are getting more oxygen over the filter, therefore better biological filtration.

Got it?

I do not know what I must do to make this clearer, and as far as I am concerned sketches are not going to help either.

Kind regards,

Dirk

 

*Lightbulb moment again*

If you are running a single chamber 20 x 80 x 20 (as per your example), the AREA of initial filter floss which does the mechanical filtration is much larger... thus takes a lot more time to clog up. Thus the water passing through the ENTIRE SINGLE chamber is oxygenated. Thus we are giving the bacteria oxygen to survive, thus they can take up the ammonia and nitrites.

In the up-down set up, the single chamber AREA is a lot smaller, thus gets clogged up much faster, also preventing oxygenated water getting to the bacteria. Therefore the bacteria is not at it's full "potential" and we are simple creating a very effective mechanical filter, with poor biological. The water getting to the bio-filter, although being full of food for the bacteria, doesn't require the oxygen to keep the bacteria alive!

So again this comes down to it doesn't matter what the flow-rate is... because granted, in both the up-down vs the single chamber you would have the same inlet and pump rate, but the effectiveness of the filter comes down to HOW you lay it out, and HOW effective your set up really is.

 

Hi Ashley,

whilst you were adding your comment, I wrote another which got lost on submission, but this does not matter, I am glad to see that you are seeing the light.

The point that you make about giving the bacteria more oxygen is the most crucial, in a narrow bore filter this is where the limitation lies. Exactly as you say, the filter is not getting to its full "potential", the surface area is there, but the oxygen is not so it cannot work in terms of biological filtration which is the most critical.

However, your last point about the flow rate is correct, but the actual speed of the water flow through the large surface area single cell filter is SLOWER, which is what is critical as it is this which makes it more effective.

Kind regards,

Dirk

 

Maybe I should add my early comment nevertheless:

Let us say that you have a tap of which the maximal flow rate is 200 litres per hour. You have two hoses, both are 20 m long, the one has a diameter of 1.25 cm (the old 1/2 inch) and the other 2.5 cm (the old one inch). You use Gardena fittings on both hoses and you use the same sprinkler on both hoses. Now you connect the thin hose with the sprinkler onto the tap and open fully and measure the height to which the water from the sprinkler sprays. You then take the thick hose and connect it up with the sprinkler onto the tap, open fully and measure the height to which the water from the sprinkler sprays.

With which hose are you going to measure that the sprinkler has a greater height and why?

My Sunday afternoon riddle!

 

The bigger hose. less friction?

 

Guido: Glad we are getting this across, now back to my hose pipe question:

No Mic.E, friction of the hose has nothing to do with it.

Tip: Think about what you were taught in school physics, F (force) = p (pressure) x A (area)

 

One last question
I have to build a new sump and if you look at the scatch I will aerate the "Overflows"
The first chamber I will use filter-wool, second : course brick gravel or ceramic tubes and if I do a third, I thought of relative fine sand??

 

It is obviously the larger hose. Same principle than with a nail or pin-head needle.!

 

Hi Guido,

No, you must NOT built a sump with three chambers, build a sump with one chamber, that is just what I have been trying to bring across to you, put ceramic tubes such as Siporax in the bottom and a filter sponge or filter wool over the top to do the mechanical filtration and that is it! Far better than three chambers, believe me.

You are correct that the bigger hose is going to cause the sprinkler to spray higher, but I still want to know why? My father was an engineer so I was brought up with engineering principles, so I was taught such things from an early age, but can you guys come up with the reason and the answer?

Kind regards,

Dirk

 

The bigger hose because more volume of water can pass through it at once... even though the pressure coming from the tap is the same, and the same "back pressure" from the sprinkler in both hoses are the same, you have more volume going through the bigger hose. (I remember my science teacher trying this question on us in matric... can't quite remember the exact scientific answer... but I know it's the bigger hose.)