Flowrate ...high or low?
 

There were many comments on the number of turnover for sump setup. From the web, there are many articles on this and 4x is the ideal turnover for most cases, little explanation on why this is so or is it really the ideal case? Many hobbyists follow this rule of thumb. My question is ....why 4x and not 1x, 2x, 3, 5x, 6x ...etc??? Does it really matters??? Does flowrate affects the water parameters???

Let us look into a typical setup:
tank: 522
sump: 3x1.5x1.5
Media: wool and CR in 1st compartment. 2nd/3rd compartment, CC n CR.
Bioload: 20 mg/l of nitrate per week.

To understand the flowrate, one has to look closely on the followings:
- the fish respiration n excretion
- the nitrification process of the bbs
- the dynamics of sump


Let us look into the eco system.

1. Fish respiration and excretion (using ARO as the subject).

Fish requires oxygen and obtain it mainly Dissolved Oxygen - DO - in water. The excretion comes in 2 form....ammonia and solid waste. Ammonia excreted via the gills and anus whereas solid waste via the anus. Simple?


2. Nitrification by BBS.

Beneficial bacteria ...commonly known as bbs, these group of bacteria are responsible for nitrifying ammonia to nitrite to nitrate. These are mainly obligate chemolithotrophs. This simply means that they must use inorganic salts as an energy source and generally cannot utilize organic materials. They must oxidize ammonia and nitrites for their energy needs and fix inorganic carbon dioxide (CO2) to fulfill their carbon requirements.


Ammonia to Nitrite (ammonification)
NH3 + O2 --> NO2 + 3H or

55NH4++ 76 O2 + 109HCO3- C5H7O2N + 54NO2-+ 57H2O + 104H2CO3

From the simple equation, oxygen is extracted from the DO and binds the Nitrogen to form nitrite - NO2. The 3 hydrogon ions will bring down the pH.
From the complex equation, ammonia (NH4+) is combined with oxygen and hydrogen carbonate to produce bacterial cell mass, nitrite (NO2-) , water and carbonic acid.


Nitrite to Nitrate
NO2 + H2O --> NO3 + 2H or

400NO2- + NH4+ + 4H2CO3 + HCO3- + 195 O2 C5H7O2N + 3H2O + 400 NO3-

From the simple equation, hydrogen ion is again released and thus contribute further to the lowering of pH.
From the complex equation, nitrite is combined with ammonia, carbonic acid, hydrogen carbonate and oxygen to produce bacterial cell mass, water and lots of nitrate (NO3-).

Why the complex equations? Two important points that come out of these equations.
1. Approximately 4.3 mg O2 are consumed for every mg of ammonia-nitrogen oxidised to nitrate-nitrogen!!!
2. 8.64 mg of alkalinity in the form of HCO3- are consumed per mg of ammonia-nitrogen oxidised!!!


Solid waste

Solid organic, nitrogenous, waste material (a.k.a.- sludge) is converted to ammonia through mineralization.
It is accomplished by any of a number of species of heterotrophic bacteria. Species from the genus Bacillus are the most common. They belong to a group known as heterotrophic bacteria and under optimal growth condition, it can reproduce in as little as 15 minutes to 1 hour. It requires oxygen too.

From the above, it can be seen dissolved oxygen is consume by the fish and the nitrification process. pH will be lower during nitrification with the introduction of hydrogen ions.


Interesting facts or myth on water management

1. Ammonia and nitrite are not the only waste produced by fish

2. High levels of organic and inorganic compunds are not directly dangerous but they encourage diseases and affect the overall water quality.

3. It does not matter on whether the solid waste decomposing inside the tank or filter, it still pollutes the water.

4. It is essential to remove solid waste from the filter and tank before they have time to pollute the water.

5. The more polluted the water, the more retention time is required in the filter.


Let us look at the sump.

It is basically a dedicated container to house biological, chemical and mechanical media.
- Biological media to house bbs
- Chemical media to absorb or adsorb contaminants
- Mechanical media to trap solid particles/waste

For most cases, biological and mechanical filtration are all we ever required. Let us look into the whole tank eco system. For simple calculation, 1kg of fish food = an approximate of 37gm (37000mg) of ammonia and faeses. If we feed 200gm of food food per day, we should get about 7400mg of ammonia. This is 7400/24 = 308mg per hour. In other words, if the ammonia is not removed within a day, we will get 7400mg in 524 litres of water (a 522 tank of 90% volume minus the sump = 524 litres of water) or a concentration of ammonia at308/524 = 0.59 mg/l!!! The Sera test kit only measures up to 10 mg/l.

Here comes another interesting part. Since bbs require time to nitrify both ammonia n nitrite, the longer the retention, effectiveness increases. The "Retention" denotes the polluted water resides within the biological filter. This present another problem!!! Ammonia is constantly introduced into the water and must be removed immediately to prevent accumulation to toxic level. This leads to the term called "Turnover".

If we can remove the ammonia the same rate as it is produced, we can have ammonia in zero value! If this is so, we used a pump of flowrate at 500 l/hr as an example; 308/524 x 500 = 294mg of ammonia removed per hr....leaving about 14mg in the tank.

If we increase treble the feeding to 600gm, we will get 924mg of ammonia per hr. With the same flowrate, we will remove 924/524 x 500 = 882mg of ammonia and leaving 42mg in the tank. From here, we can see the effects of increase stocking or feeding!!! Please note that the examples are based on over-simplification of what actually happens. There are still many factors that affect the nitrification processes.

Flowrate is an important factor in determining the removal of ammonia.

Other factors affecting the nitrification process (sump only).
- temperature
- pH
- level of DO
- types of bio-media
- qty/volume of total bio-media
- design of sump
- placement of bio-media

Temperature - It affects the growth of the bbs.
- Optimum growth is between 25 to 30C.
- Growth rate decreases by 50% at 18C.
- Growth rate also decreases at 75% at 8C
- Zero growth rate at 4C
- BBS die at 0C
- BBS die at 49C

pH - It affects the growth of bbs and toxidity of total ammonia
- 1 unit increase in pH increases the NH3 about 10 folds of the total ammonia
- pH below 6 will inhabit the nitrification processes.

DO or Dissolved Oxygen - Nitrification requires DO.
- when the saturation of oxygen exceed 80%, maximum nitrification will exist
- when DO concentration drops to 2 mg/l, nitrification stops.

Types of bio-media - there are many types of media.
- More surface, more place for bbs
- Bigger pores, easier to bring pollutants to the bbs.

Qty/Volume of bio-media - affects the retention period.
- the smaller the qty, the longer the retention per cm3
- the larger the qty, the shorter the retention per cm3

Design of sump - affects the effectiveness of the bio-media.
- The most important aspect of a well designed sump is the water transfers between the chambers.
- There is little point of having expensive media if the media is not utilised properly.
- The design of a filter system should be such that water passes evenly through all the media and not just one
end or through the center.

Layout of Bio-media - affects the effectiveness of bbs
- enable the water passes evenly through all the media and not just one end or through the center


Cons of Low Flowrate or Low Turnover
- if the turnover is lower than rate of ammonia produced per hr, you will have accumulated ammonia in the tank.
- DO is limited. The prolong retention will reduce the effectiveness of nitrification due to reduce DO level.
- Reduce the releases of carbonates/bicarbonates. It will lower the pH faster.
- Retaining of CO2 increases and thus increases the carbonic acid level.

Cons of High Flowrate or High Turnover
- increase in volume of bio-media to overcome the required retention period
- livestock might be stressed due to high water movement
- higher rate of dissolving solid waste


Looking at the various cons, high flowrate/turnover has greater benefits than low flowrate/turnover. The reasons are:

- ability to replenish DO level when the water is transfering between chambers - max nitrification.
- ability to drive out CO2 when the water is transfering between chambers. CO2 is unstable in water.
- the above 2 points will reduce the lowering of pH.
- the faster rate of releasing carbonates/bicarbonates from Coral Chip or other sources. This will mob up loose
hydrogen ions faster.
- lessen transient ammonia spike.
- increases the water turpidity.


Bottom Line:

To maximise the benefits of high flowrate/turnover, the biofltration must be of suitable size and sufficient bio-media with proper layout.

Increasing the flow rate through existing biofiltration will almost certainly improve average water quality and spreading the feedings out over the day will lessen transient ammonia spikes.

I'm no expert, but maybe the 4x is through trial and error (aka research) by the filter makers to determine the ideal turnover to allow the BB to colonise efficiently and/or for the waste in the tank to be filtered? :o

IMHO regardless of the flowrate, 1 of the main reason is how fast the the waste is clear to the Sump once it is produce by the fishes, some tank setup may take half an hour due to the return pump used whereas others may take much longer becoz of a lower output pump.

As it maybe quite unsightly for some to see the waste floating around, some just don't mind, from my understanding, once BB's are mature, it would be quite difficult to flushed them out with a fast flowrate than again i maybe wrong :o:p

Personally i prefer a faster flowrate, debris get cleared faster but in terms of BB's maturity, mine took as long as 6 - 8 months for a 5' sump, at least that's what i felt when i see my fishes and water.

Yes, I also observe that a faster flow rate 'cleans' up the tank more quickly and makes the water visibility much clearer.

But why 4X and not 10X?

personally I prefer faster flow-rate pump and do not over-stock fishes

An over-power filtration is better than over-stock bioload :D

If it's 10X, your fishes will probably suffer from the turbulence. :)
I believe a rate of 3-4X is adequate.

Hmmmm....from the various replies, it seems that solid visible waste is the much concern subject. I beg to differ. What you cannot see is the critical issue!!! There is a saying ...clear water does not denote good water.

I personally having a estimated of 2 x flow rate for my current setup.

It use to be about 4 x the flow rate but found that the there are always trances of NH4 and N02 present in the water.

As I was using two pumps, I changed one of it to a lower flow rate and added a wave maker to help circulate the water.

I found that with a lower/slower flow rate, the NH4 and NO2 became zero (tested a month ago) except after heavy heavy feeding of squid and MP where there will be a rise in these two readings...

There seems to be little or no poo poo at the bottom of the tank also.

So... please advise is my setup right? Thanks....

To me, 4 x flow rate is just serve as a guide. Its not wrong to have 3x or 5x flow rate.

Types of filter used also plays a part. (e.g: ohf, canister, sump etc)

For me who is using ohf, as long all the rain bars have water splashing out instead of dripping down is considered sufficient. :)

I no expert but just wondering is it possible for the following reasons ?? :
Faster flowrate is good for mechanical filtration - to remove solid waste/unsightful particles;
Slower flowrate is better for bio-filtration - to provide adequate time for the BBs to do the jobs. :p:o
If so, the best of all is to have a system with control of flow for bio or mech filtration. :D

Hey stoner interesting useful info.meaning the BB in the biohomme works more efficiently when the flow rate is slow? anyone can confirm?

i am using 4000l/h for my 5ft OHF, i feel its pretty decent thou the overturn rate is over what many bros suggested. also think about the FlowRate which it has to bring up to the tank for those with sump and shorter distance for those bros with OHF... so far there has been no spikes in all my NH...blahblah readings... very stable all along unless i add a new fish/water. =) but it clears up very fast.

In short, fast flowrate good for mechincal filtration while slow flowrate is good for biological filtration. That's one reason why I got slower rate flow in my house filtration system and yes... the dirt is unsightly in there and need much longer time for them to be "suck" away.

It simply means that your biofiltration is not sufficient for higher flowrate.
The rise in total ammonia during heavy feeding is called transient ammonia spike. This can be reduced by spreading the feeding....Instead of 1 heavy feeding per day, change to 3 feeding instead.

OK... noted and understand.

Current 6 x 2.5 x 2.5ft is supported via a small 3 x 2 x 1.5ft sump. A new 5 x 2 x 2ft sump is on the way...:D

Thanks for your advise...:)

so bro Mod atom, can let us know why the sump pump is 4X the tank volume? really interested to know :) Is it a bad idea to have 10X?

He...he... I only have 1kg + inside my sump.... the rest of 10 over kg are cheapo CC ....:D

4x is just nothing more than a guide. You can have 10x but you must have large sump with sufficient biomedia to compensate for the reduced retention period. I prefer high turnover. 6 to 8x will be nice.

An exaggerated example:

The water speeding pass a chamber containing CR at 1000 l/hr, can remove 4 mg/l of ammonia.
When the velocity increases to 2000 l/hr, the chamber can remove 2 mg/l of ammonia.
To compensate for the losses, the water has to pass 2 chambers in order to remove 4 mg/l of ammonia.

I use a x12 flowrate with a 1000/hr pump using OHF and a 1300/hr canister for my 3 feet tank. Its an overkill but it keeps the water clean and my puffer seems to be okay with it :)

Im thinking of just getting one good canister like FX5 instead of running two at the same time

A very clear explanation... :D

Sweet!:)

understand now. Is there a minimum limit to the sump size to have a good filtration? Basically, what is the minimum tank size recommendation for using sump method of filtration? 3ft main tank with 2ft sump tank?

Thank u 4 the clarification very clear now ....cheers..:)

prof atom, very interesting & valuable lesson again ...




i'm using an atman 8450L/hr for my 6X3X2.5ft with 5X2X1.5ft sump. turn over is ard 4.5X after pressure loss to height & elbows. water is crystal clear ...

also using a MeBner 6000L/hr for my 6X2.5X2ft tank with 4X2X1.5ft sump. turn over is abt 6X plus ...

no worries abt water quality.
now looking at ways to reduce NO3 without using denitrator, like optimising biohome fully using bigger compartment chamber to reduce flowrate thru media ...:D:D

Anthony

Perhaps you could propose a sump layout design which you think would be optimum in filtration?

I find the most effective method for limited amount of space is to use denitrator but ....it is not that simple and costly too.

Actually ...most of the designs by the popular tank makers are works well. The problem is the laying of the biomedia and the water level.

Hahaha.. well perhaps using those standard designs, you could advise on the optimum biomedia layout?
Base on normal as well as heavy bio-loads perhaps?

My opinion for sump turnover is ... "as fast as you can afford".

Here's my reasoning,

Bio media is not single pass filtration. E.g Reverse Osmosis. Where the water only have 1 chance of passing through the media.

Bacteria will have higher efficiency when in higher waste concentration assuming carbon is not the limiting factor.

Eg. Both 100mg/l and 10mg/l of NH3 is passing through the same media with same flowrate. In terms of percentage NH3 removal, the 100mg/l will have a much higher efficiency than 10mg/l.

By introducing a higher flowrate, you are narrowing the gap towards perfect water circulation. The main idea is to bring higher concentration waste water(from main tank) to the bio media as fast as possible

Alot of pumps available in the market are rated at 0 head loss so you will not get the rated flowrate. Depending on the pump you use and headloss, flowrate can be reduced drastically to only 10-20%.

Biomedia and piping will clog overtime and that will reduce the flowrate further. So my opinion is, go for the highest flowrate and better quality pump.

Hi bro, I'm still not very clear can you elaborate to us.
So High/Low flow rate, big/small sump tank and more/less medias are good?
An understanding of concept is more important. Tks.

An exaggerated example:
The water speeding pass a chamber containing CR at 1000 l/hr, can remove 4 mg/l of ammonia.
When the velocity increases to 2000 l/hr, the chamber can remove 2 mg/l of ammonia.
To compensate for the losses, the water has to pass 2 chambers in order to remove 4 mg/l of ammonia.


let me try , the above mean
flow rate (1000 l/hr) + chamber remove ammonia.
1 + 1 4 mg/l
2 + 2 4 mg/l

double flow rate require double chamber to remove same amount ammonia.

flow rate in two tank (main tank and sump).

Main tank => higher flow rate pump(not till stress the aro) require for push the poo poo and ammonia to sump.


sump = > maintain optimium flow rate for BB to grow and nitrifying ammonia to nitrite to nitrate. the question is how to maintain as time to time the 1st, 2nd , 3rd comp will clog or slow down the flows.....

by adding flow meter to monitor the flow rate in each comp? and regular sump maintenance once flow rate affected?

the objective is to reduce or remove ammonia and nitrite lvl in sump before back to main tank.

whoa...very heavy discussion .... my simple opinion: 4x turnover recommended based on the usual sump size used by hobbyist generally, if hobbyist can afford to have a bigger than ordinary sump (means higher costs :D) its definitely better to opt for higher turnover rate (again higher costs for a stronger pump)..... I personally prefer higher turnover :D

Yes.....as what I had mentioned, it is just an Exaggerated example for easier understanding.

I'm not a very chim person but this is what I do and believe.

Heavy mechincal filtration (thick layer of wool) before hitting the biological filter media in filter system. Flowrate can be fast but one must remember that the wool may choke and water can't pass through them as good as they are new.

But if flowrate is high and filter wool is not doing the mechincal filtration well enough, dirt will start pushing through and they will all start to choke the media underneath. Fast flowrate work well if the surface of the mechincal filtration is huge. If small chances of clogging is higher.

Just the way I keeping my fishes.:o

refer to Koji bro, 2nd comp should have wool ontop as well. as better flow rate evenly flows from 1st comp to 2nd comp.

like humans need time to do work, bacteria also need time to do work.

too little time, the work is half done
too much time, does not mean more work is done.

sounds logical that we want to bring solid waste( solid== concentrated)
to biomedia to have higher waste difference.

but do note that with higher Flowrate, the breaking down of waste into finer( hence less concentration) is also faster, don't think that bacteria action on the waste will be faster than the mechanical breakdown of waste. in the long run, the investment in higher flowrates might not yield better results

But if the first compartment is well stock with filtration wool, the 2nd compartment can be well stock with media rather than adding more filter wool.;)

When looking at the filtration system, one must look at the whole picture and not just 1 subject of the picture. Let us examine the some of the popular topics:


Solid waste in the tank.

2 ways. Remove it manually or use a blower to push it to the filtration system. Though higher flowrate has an indirect effect in solving it but only partially.


Trap waste collected on mechanical filter.

3 ways of looking at it.

a. Clean the filter daily to prevent any solid waste from mineralisation. If the solid waste is remove physically, the ammonia will be much reduced.

b. Clean the filter frequently such as once a week. In biological point of view, a group of healthy and sufficient heterotrophic bacteria can break down the waste within a day. They can increase their numbers very quickly if the solid waste increases. In other words, cleaning the mechanical filter once a week is "better than not doing" at all. Does this means that we should forgo the mechanical filtration? No!!!

- Mechanical filter helps to prevent visible waste from clogging the bio-media.

- Heterotrophic bacteria excrete slime while minerialising the waste. If we allow the solid waste to breakdown at the bio-media, it will clog super fast.

c. Don't clean at all!!! If the population of heterotrophic bacteria is more than sufficient to breakdown the solid waste, it will attack the sludge too (DO must be high). If you look at a good bakki shower, you will hardly see any sludge or slime. I change my wool once in 3 months not because it choke with slime (in fact there are hardly any slime at all), it is due to habit. The trick is ......do not submerge the wool and must expose to fresh air.


Flowrate vs Rate of removal of ammonia

All medias are not equal. Some have more surface area than others. Some have smaller pores than others. Some are square, some are round ...etc.

In one setup, all the chambers are filled with jap matt only. In another setup, all the chambers are filled with CR. Since CR has more surface area than jap matt, it can be deduce that the setup with only CR has more bbs than the setup with only jap mat. This means that the setup CR can afford to have higher flowrate than jap mat. Reason .....due to the lesser bbs population in jap mat, it requires longer retention period to remove the same amount of ammonia as in CR.

Look at those fgt filter box for pond. For most setups, They contain mainly jap mats or similar products. If compare with those 3-5' sump for aro tank, the flowrate is much slower ....flowrate vs size ratio. Why? This is because the retention period has to be longer as the media used has lower surface area than those exotic bio-media commonly used in the sump. If you look closer at the jap mat, it contains lot of sludge/slime. If you look at those exotic media in our higher flowrate dump, you could hardly find them. Although this is not exactly a good example as most of the fgt do not use filter wool for the initial mechanical filtration, it is still close enough.

The end result, we are just turning the toxic waste to nitrate!!!

Water management for fishkeeping is a matter of "give and take". We have to prioritise on the Do's and Want.
Filtration system for fishkeeping is similar to mother's nature filtration system. Not 100% or even close but similar. We cannot mimic 100% due to cost, space constrain and man's "greediness plus selfness".


To be continue ...gone fishing!

well said....the key is "not to submerge the wool..."..... I find this practice to be most useful...it really does wonders..:D