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Discussion Starter · #1 ·
Looking at upgrading from my sucky little internal to a canister filter. I have a few different models in mind, but the issue I have is ACTUAL flow rates. We all know that a canister (or any Powerhead) has a max head height for which it remains effective. What I need to know is some sort of formula for calculating flow/pressure loss over a particular height, through a particular diameter of hose...

An example; I buy a Canister filter with an advertised flow of 700lph, and max head of 1.8m. It sits in a cabinet approx. 600mm below the water surface and flows thru 17mm pipes. What is the actual flow felt by the little fishies in the tank? Variables to ignore: spraybar hole size; level of gunk present in the canister...

Finally, I intend to DIY an inline CO2 diffusor at some stage. If I have in mind a canister that will see a (advertised) flow of 500lph, would I be best to go to a 550 or 600 to compensate for the future flow loss induced by the inline diffusor? Or would the loss be so minimal as to not be an issue? I realise this question is completely arbitrary and relies on many variables, so a general idea response will suffice.

Cheers in advance.
 

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Some companies are a lot more conservative about their specifications than others are, and some pump designs are less prone to height related flow rate drop than others. Some pump designs will push their rated flow through a pinhole while others are prone to serious drops due to back pressure.

So the only way to be certain is to use a bucker & stopwatch to assess flows (or look up someone who has).

You may also be able to get a hint by asking the vendors on your "short list" about how they arrived at their rated flow specifications...
 

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If you can get the manufacturer to cough up the pump's operating curve you can actually evaluate it fairly well just knowing what that curve looks like. I have never seen one for a piece of aquarium equipment but use them all the time in other places.
The height of the tank compared to the location of the pump has nothing to do with the pump's head. What matters is how much flow restriction exists in the tubing, filter, spray bar etc. The only effect of elevation on the impeller is that if the level in the tank is lower than the level where you return water, the difference needs to be overcome with pump head the rest of the head is used to push water through the filter, tubing and spray bar.
 

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If you can get the manufacturer to cough up the pump's operating curve you can actually evaluate it fairly well just knowing what that curve looks like. I have never seen one for a piece of aquarium equipment but use them all the time in other places.
The height of the tank compared to the location of the pump has nothing to do with the pump's head. What matters is how much flow restriction exists in the tubing, filter, spray bar etc. The only effect of elevation on the impeller is that if the level in the tank is lower than the level where you return water, the difference needs to be overcome with pump head the rest of the head is used to push water through the filter, tubing and spray bar.
I hate to admit this, but I never thought of that before! The inlet pipe to the filter is full of water at all times (it is a siphon), so the pressure at the canister filter is the height of that column of water. And, that will, in most cases, be the same height as that of the return pipe, also full of water. So, the filter pump has its entire head pressure available to overcome flow restrictions in the return pipe. So simple, and I always figured the height of the tank over the filter was a critical parameter.

Carrying this logic a little further: when the filter manufacturer says the tank has to be at least X feet above the filter it just means that the pressure of the water in the canister filter has to be above some value to avoid cavitation. So, that's why Mulita's bar aquarium with the filter just a bit lower than the tank works so well.

Is my reasoning all correct?
 

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Discussion Starter · #5 ·
Rather than start a new Thread for the same topic, I thought I'd be Internet environmentally friendly and recycle this one...

So, here is (another) pic of my 70. As you can see, I've done a little rescaping, and everything seems to be coming along nicely.



With a DIY 90L Betta barracks in the works, I need to raid that abomination of a filter seen in this pic (yes, the sucky one mentioned above...) to run that tank, and replace it with said Canister for the 70...

So. My question is this: How should I orientate the intake and outlet of the Canister in this tank? The obvious option would be to mount both on the right side wall, sending water toward the Stricta on the left and then back again. However. I had the thought to mount the in/out takes on the left side, with the intake down amongst the Stricta, and the outlet flowing across the top of that plant. The idea being to promote better water flow thru the dense areas of the tank... What do you think? Of course, doing it this way will leave the right side looking rather bare, but I can deal with that, I'm sure.

There is also the option of mixing it up a little, ie; intake on right outlet to the left or vise-versa...

Thoughts please??
 

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This is another very basic question that I haven't seen explored nearly enough. For what it is worth, I now have my canister filter outlet near the top of the tank, in the left rear corner, aimed diagonally across the tank and pointed slightly up to create a little ripple on the surface. The filter inlet pipe is in the same rear left corner, but down near the bottom. My logic was to get the surface ripple to help keep oxygen in the water and to keep the surface clear of scum, plus to try for a top to bottom circulation to complement the around the tank circulation I get from a Koralia powerhead mounted in that same corner of the tank, but down near the bottom.

I can't remember ever seeing a well written discussion of the pros and cons of various locations for the inlet and outlet.
 

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Discussion Starter · #7 ·
Right-o. So, I am expecting my new Canister on Monday (actually hoped it would be here for the w.end, but nevermind). I've been puzzling over how I'd go about performing the changeover between old and new, for the past few days. My thoughts/ideas/ponderings are thus:

Do I...
1) Leave the Internal in place, but remove the impeller from within, and set the Canister to draw thru the (now inoperative) Internal (it has an outlet tube that'd be very easy to plumb onto), with the intention of building bacteria in the Canister?
2) Remove the Internal, and place all media from within into the Canister to help build bacteria?
3) Have the Internal and Canister going in unison for a week or so until bacteria has colonised the Canister? Or,
4) I'm thinking about this way too much! Just turf the Internal, and start up the Canister, all those plants will take care of buffering any Ammonia issues, so there's no need to worry?

I like the last one, although I know it's risky, however I'd like to keep the bacteria in the Internal alive, some how, whilst I construct the Barracks and relocate it to that tank. This would make options 1 to 3 the more preferable, but which one??
 

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I vote #3. I did that when I added my canister filter. Ran my HOB and canister simultaneously for a week and removed the HOB. But I eventually put the HOB back again for the added flow.
 

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Option 3, but leave them running together for longer than a week.
When you are ready to use the little filter for the Bettas you will not have to disassemble anything like if you had gone with options 1 or 2.
Ultimately number 4 will come into play, but better to at least try to get some bacteria going in the canister before invoking option 4.
 

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Since you're filtering less that 30 gallons of water, how about getting a Magnum 220 and calling it good? I've always used Magnums and never had much bad to say about them.
 
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