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.

[ecoquest]

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?

[alf88]

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

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.

[ecoquest]

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

[canopy]

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

[ecoquest]

Originally Posted by canopy

But why 4X and not 10X?

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.

[stoner]

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.