Filtration rates, flow, and other questions

Good day Professor,

I've noticed there has been a lot of talk as of late on TASA with regards to filtration, sumps, sump set ups, filtration rates etc etc... and whist a lot of information that has been provided is sound, and correct, I also feel that some of the information is a hit and miss. Let me expand a little before asking your opinion:

In my tank, I run a 1100lph Canister filter, but because the canister sits lower than the recommended height, I fear that I am possibly getting about 800 - 900l/h max out of this canister. This is only 3 times my tank volume, however we always advise new members to aim for 5 - 10 times. (Which is actually a very broad range to aim for in my opinion.) But then when you look at my tank, it is always sparkling. I went 4 weeks recently without a water change (that end of the year rush...) and after testing, my nitrates were still at zero. According to the theory, and some members opinions, if I am only turning my water over 3 times an hour, my nitrates should be climbing.

It is often assumed that a sump should be designed in an up/down fashion, with each chamber getting lower in height so that the last main chamber (with the heaters, return pump, and sometimes airstoned) is only half filled. This is to allow for excess when the power goes off and excess water is syphoned out the tank. (I think it's just a way to prevent flooding). My logic tells me that water will always take the path of least resistance, so I do not see how this up/down can be the most effective. The water will not necessarily pass over the entire media. And as you have also stated, the up/down also slows down the flow rate.

Now here comes my logic---
When you are filtering water (the filter bottles we all have in our fridges), logic says that the SLOWER the water passes through the filter, the better filtered the water will be... however in fish keeping, we all aim for higher flow rates, and try get as much water to pass over the little bit of filter media we have as quickly as possible. Is this not just defeating the object?

Would passing water over a larger volume of filter medium, at a slightly slower rate not be more effective?

How would you then design a sump? (I noted you said in a thread recently that you don't like the up/down traditional design. And this has been mentioned to me by Dolphin as well in past conversations.)

I also agree the water movement in the main display tank is essential to fighting algae, and obviously certain fish prefer faster moving waters... but this doesn't necessarily have to be accomplished through the main filter. In my tank I have 2 unobtrusive internal filters to assist with water movement, because my canister is not providing the currents.

Trust this will provide some thoughtful insight to the start of 2011....

Regards

 

zoom well asked..i had a few questions about this the other day and would still like more clarity because im building a 1000l cichlid tank and want it perfect (for the fish ofcourse)

 

Bump!

(Not sure if this one slipped your beady eye Professor?)

 

Zoom Im totaly with you on this one.

at the moment im helping a friend of mine to build a two canisters for filtration for his 4ft. it will consist of two chambers of 110mm diameter and 1000mm tall with a volume each of 9.5L. the one chamber will only be batting for mechanical filtration and the other is 1mx3m 40% shade netting rolled into a sausage of 1m tall to fit into the other chamber to give nice surface area for the bio filtration. These two large chamber/canisters give huge surface area for filtration with a 2000l/h pump.

when deciding on filtration you should take into account some variables:

flow rate (L/H) vs filtratrion area (mm2) vs tank volume vs "the other stuff": fish crap+over feeding

i think theres no such thing as over filtration, maybe to much current in a tank

 

Size of fish, stocking numbers, species, planted or not, tank depth, canister above or below tank . . so much more stuff to consider

TM

 

ok..please elaborate on the difference on the canister being above or below the tank...

(am watching this thread very closely)

 

If the canister is below the tank . . the motor works harder at pumping the water UP to the tank. . flow rate is compromised. If the canister is placed above or in line with the tank. . the flow rate will be at it's peak.

 

@TankMaster... whilst I understand your logic, I disagree entirely. Most of our canisters work on gravity to feed them, and the pump to pump the water back up. If we place the canister above the tank, or even level with the tank, the gravity will not feed the canister. I agree that the pump will create a suction if the canister is properly sealed, and will suck water into the canister, but here you are creating exactly the same pressure on the pump... instead of it pumping back at a higher height, it has to suck the water in from below the canister.

The aim of this thread is still to find out what should we really be looking for in a good filter with regards to flow rate versus filter medium/area/volume. I still maintain that a lot of our tanks filters are set up on a hit and miss scenario. If we have problems, we blame the filter. If we have a great looking tank, we thank the filter... But if we could find out according to @Dirk Bellstedt his opinion on filtration, we may eliminate a lot of issues we have with filters.

A lot of us use "commercial" stuff in our filters... like hair curlers, or pot scours and normal bath type sponges. This is often a cheaper alternative to the LPS filter medium, but I am not convinced that a hair curler or a pot scour actually benefits us in any way. I mean if it was so great, and as a cheaper alternative, why is there not something like this manufactured for the industry. I mean let's be honest here, if the Chinese thought hair curlers were an amazing filter media, they certainly would have expanded on this by now and come up with something similar in design and function?? My opinion is that 3 hair curlers take up the same amount of space in my filter as a bag of ceramic rings... but the ceramic rings offer so much more surface area... so why go with the curlers? I'm not even convinced that Bio-Balls offer great surface area for bacteria, and still think the best available filter media at the moment is the old fashioned ceramic rings.

Koi ponds follow a similar principal as a pool filter does by incorporating a sand filter in it's set up... but a sand filter on a tropical aquarium is seen as a waste of time and energy by a lot of other aquarist's. Yes Boyu have created one, but if it was so great, why is it not used more.

Again, these are all questions that we start asking when it comes to filtering, and I am sure that the Professor will enlighten us as to what he feels is the most effective way when you take rate vs area vs actual method employed. I'm also very interested to hear his take on the sump design.

 

A lot of us use "commercial" stuff in our filters... like hair curlers, or pot scours and normal bath type sponges. This is often a cheaper alternative to the LPS filter medium, but I am not convinced that a hair curler or a pot scour actually benefits us in any way. I mean if it was so great, and as a cheaper alternative, why is there not something like this manufactured for the industry. I mean let's be honest here, if the Chinese thought hair curlers were an amazing filter media, they certainly would have expanded on this by now and come up with something similar in design and function?? My opinion is that 3 hair curlers take up the same amount of space in my filter as a bag of ceramic rings... but the ceramic rings offer so much more surface area... so why go with the curlers? I'm not even convinced that Bio-Balls offer great surface area for bacteria, and still think the best available filter media at the moment is the old fashioned ceramic rings.

@ Zoom: Ceramic rings is probably the best surface area for bio filtration, but the price....R80 for a small box, bio balls defnitley to expensive aswell and i doubt if you truly get that much surface area, ive got two canister filters with pot scourers, the one is a diy filter out of 110mm pipe about 400mm tall with a 250L/H on it for my 60L planted, their is about 24 in their, this works, i havent had noticeble problems yet, the other canister is a vluval 400l/h (thanks singularity) on another 60L planted in the botom tray the sponge/mechanical filter that came with it, and in the top tray their is about 10 scourers, also no visible problems. If I had the money I would defnitley have bought a box of ceremics.

 

Also watching this post very carefully....

I agree that BIO balls are pretty average - ceramic rings from personal experience work great....

In my Angelfish tank I use stones (like building stone) and some roof insulation in the filter/sump and the water is crystal clear

Just my opinion here - no science involved

 

Indeed you are correct sir, if you open most canister filter manuals they will tell you the peak low rates when they are empty and level with the tank and that is the max rating they put on the box. Conversely they also give the flow rating for when the canister filter is standing below the tank and use that as the minimum flow rate. Rather useful article: http://www.firsttankguide.net/canister.php

As for filter media I replaced all of my ceramic rings with clay balls and I find them to work better.

 

Hi Zoom.
I only read this thread now, and if ok, I'll try shed some light as far as my knowledge allows.
Firstly, there is a difference in commercial canister filters and sump/trickle filters in design, volume and flow rate. Canisters are as such rapid filters passing large amounts of water throug a small amount of surface area. A fluval 304 for instance is rated for a 300liter tank, pumping 1200 liters through maybe a volume of 5 liters. These filters can be filled with sponges that promote bacterial growth, and some even have compartments for ceramics and other material. The problem with these are that they only function biologically as long as there is a continuous flow of oxygen rich water through the medium. If the pump stops all bacteria die in a relatively short time and the dying bacteria WILL poison the water if the pump is turned on without removing the water in the filtes and cleaning it.

Sump or trickle filters ideally have a much larger volume of water and medium, and also should ideally have a slower rate of water flow. Ideally one should aim for at least 10% of the total water volume to be filtered in filter material only. In other words, a 200liter tank should ideally have 20 liters of filter material. This should be made up of mechanical material (wool), coarse and fine material. The advantage to these filters are that an airstone can be placed beneath the material in the event of power outages (obviously battery driven air pumps) which will then aerate the material and prevent bacteria die-off. The total water volume then only pass once or twice across this are per hour and provide a very slow and favourable environment for bacteria growth and filtration.

As far as bio-media is concerned the following is relevant:
Natural media (lava rock, ceramic etc) have a much larger surface area than plastics do, so more bacteria per volume.

Plastic though is more hygienic in that its not as favourable for parasite growth as natural material.
One thing to take note of though is that bacteria has a life cycle where they grow on top of each other. With plastics these 'clusters' will come loose when the bottom layer dies of. It will then float away and should be trapped with a fine micron after filter. This does not happen with natural material. Natural material need to be rinsed thorougly every 4 to 6 weeks to rid them of grime and dead bacteria.

In al these filters a fine silt, due to bacterial life cycle builds up. This can be minimized by aeration from below which also prevents area's of oxygen shortage.

Hope some of this helps?

Rgds
Marco

 

yaa its helps...go on....

 

Hi dragon,

I think, to summarize, the target of optimum filtration would be a ratio of 1:1. 1 Being the water volume filtered, and 1 being the amount of filter material filtering the water. This would mean that for a 200liter tank one would need 200liters of filter material. Its just not feasable really. However, if we look at the average canister which maybe holds 3liters of filter material and is still rated for a 300liter tank, the equation jumps to 1:100, hence the flow rate has to increase to compensate for the low filtration. At 1:1 the water only has to pass the filter once every hour to be filtered entirely. I understand this is not always possible, but when building a sump, one should aim for that ratio to be as low as possible. If you use the 10% principle, in other words 100liter tank =10 liter material, you end up with a flow ratio of 1:10. Much better than 1:100 provided by some canisters.

Material could be a personal/financial choice. Though the 10% rule would apply to top notch media, and thus lower quality media will see an increase to achieve the same level. For instance ceramics at 10% and plastic bio balls at 20%. Hair curlers would be even higher. Flow rate per hour thus attempt to compensate for low volume filter material. There would be a limit to this though, but I would not know where that limit would be. Maybe at 1:200 flow rate would have to increase so much that water would pass over the media too quickly for bacteria to survive in/on the media.

 

thank you so very much that really helps...am thinking about trying a DIY canister and this info really helps

Though when i read this thread it really seems that a sumps is best because it allows more control in terms of surface area and flow control...what you think??
thanks

 

I agree that a well designed sump is the optimum to go for... however I am very happy with my current canister. It holds 15litres of water, which is more than the normal, and has fairly large baskets for material. Put it this way, I need 6 BOXES of the Boyu Charcoal to fill one basket. (That's the only thing I can think of to give you an idea of how much each basket holds.)

With my canister being lower than the tank height, I have also reduced the flow rate... and seriously seriously doubt I am getting 1100l/h out of the pump, (as the box suggests). I would think I am getting about 700-850 max. This also suits me better, and my mind still says the slower the water moves over the media, the better filtration I am getting.

@Marco , as always your posts are always welcome and very informative. Thank you

---------- Post added at 17:01 ---------- Previous post was at 17:01 ----------

I agree that a well designed sump is the optimum to go for... however I am very happy with my current canister. It holds 15litres of water, which is more than the normal, and has fairly large baskets for material. Put it this way, I need 6 BOXES of the Boyu Charcoal to fill one basket. (That's the only thing I can think of to give you an idea of how much each basket holds.)

With my canister being lower than the tank height, I have also reduced the flow rate... and seriously seriously doubt I am getting 1100l/h out of the pump, (as the box suggests). I would think I am getting about 700-850 max. This also suits me better, and my mind still says the slower the water moves over the media, the better filtration I am getting.

@Marco , as always your posts are always welcome and very informative. Thank you

 

Hi Zoom,

I agree that canisters work fine. I run one on one of my tanks too and have no problem. I think, and this can probably end in an argument, that though it is impossible to "over-filter" a tank, it is easy to "over-kill" the filter... When and if something works, its not needed to reinvent and overspend money to improve what already works. If a canister works, stick with it! And vice versa. What I like mostly about sump filters is the increase you get in water volume, which could be endless. I also find a sump a great deal cheaper than a commercial canister.

Bottom line, both has its place and functionality. Sump filters has restrictions when used in planted tanks with added CO2 as the trickling water reduces co2 in the water. In that instance then a Canister is 'better'.

Rgds,
Marco

 

shoo shoo shoo

guys thank you very very much for all the input...for a while i've been putting my hand over the "output" of my canister and it never felt as strong like the pressure from my 600l/h power head and i always wondered about this....so i did a experiment i lifted my 1100l/h canister about a foot(about a rulers height) and and instantly it created more pressure...the tank we're taking about is about 350 litres which is 900 from the floor and the 1100l/h canister was on the floor...

when i move house i'll set my tank up differently so that the canister is at the same level as the tank...

guys i went away to Bainkloof saturday for the day and when i got back my tank that was crystal clear is now super super clear...i can even see the debris flying up the "intake".

i am still to try the sump though i will consult you guys again as i am very impressed with the advise lol because it worked...

have a super day
fire

 

I was wondering now, Im using a lifetech ap 3500 return pump in my sump of about 80 liters. my tank is about 320 liters i think, and the tank is 0.7 meter from the floor, but the water gets pumped about 1.3 meters high, i wonder how many times does my water circulate in an hour? the pump didnt get a chart with it, so i wouldn't know. The petshop says its 2500l/h, but that must be when its not pumping 1.3 meters right haha. would my pump be sufficient ?

 

If the LPS is correct, and you should be getting 2500l/h @ 1.3m... then a 320 + 80 tank would be turning over 6.25 times per hour. Obviously with you raising it an extra 0.5m this would drop... and not sure how drastic your the drop off would be because according to charts I have viewed, it appears to drop off rather drastically from a certain point. I think the only real way to know if this is an effective filtration method is to watch the tank, and monitor the chemical (No2, No3) levels over a few weeks.

Maybe search the Internet to see if you can find the chart for this pump?