Looking for small canister filters

Discussion in 'Filters and Filtration' started by junebug, Jul 22, 2015.

  1. junebugFishlore LegendMember

    Does anyone know of a canister filter with GPH around 30-50? I'm looking for some, for a few of my nano-tanks and I need the low GPH. Thanks!
  2. leftswerveWell Known MemberMember

    Once filled with media and a head height of 3ft or more, the sunsun hw603b goes down to about 50gph. It has a shutoff valve that could be used to lower it further, but once it gets used some, it probably goes down in gph even more.

  3. BDpupsWell Known MemberMember

    Your best bet would be to get the smallest canister you can find and put a ball valve on the output hose if it doesn't have shut off valves, then turn the valve until you have the desired flow. The Toms mini rapid canisters are 80gph.
    I'm not sure if you could get a ball valve on one of those. I've never used one. But there are small Eheim classics 2211's ,60 gph, that could easily have a ball valve put on them. If they don't already have them on a quick release valve. I'm not sure if these have the valves included with them like the larger classics.  
    But as already mentioned when the filters have media in them the gph does decrease as well.
    Sent from my iPhone using Fish Lore Aquarium Fish Forum

    Last edited: Jul 22, 2015
  4. JsigmoWell Known MemberMember

    Better to use a separate ball valve in the outlet (return line ) of the filter to throttle the flow rather than the quick release valves, because that way, you are only restricting the outlet of the pump, not starving the inlet, too. This helps prevent cavitation and bubble formation within the filter.

    Also, head height won't affect flow rate through a canister because they're sealed, and therefore "see" no static head. The down tube's water's "weight" balances the up-tube's water's "weight".

    What will affect the flow is the friction loss in the tubing or fittings, so it can appear that it's the elevation difference, when its really just the tubing length at play.

  5. BDpupsWell Known MemberMember

    Eheim has separate valves for the input and output. Adding another valve would be redundant.

    EDIT: Drilling the holes out bigger on the spray bar actually works better anyway. Restricting the flow may damage the motor. And this can be done on any filter with a spray bar. No need to have to purchase anything else.
    Last edited: Jul 22, 2015
  6. leftswerveWell Known MemberMember

    The little sunsun HW603b has the valve on the output of the pump. The pump is mounted external to the canister, that way if the pump fails in the future, you have a nice prefilter for your main canister. Because of it's set up, head height does matter with it. The pump is at the bottom, not the top, so it has to push the water back.
  7. SnyperToddValued MemberMember

    It doesn't matter where the pump is in the filter, as Jsigmo said it will see no static head. It's a sealed system, the siphon effect of the water coming into the filter does most of the work pushing the water back into the tank. If it was an open system like a sump you'd have to factor in head, but with any canister filter, the water coming in has nowhere to go but push the water already in the canister back into the tank.

    Also, as these are non-positive displacement pumps, slowing the flow will not damage the motor in any way as long as enough water is flowing through to keep things from overheating.
  8. JsigmoWell Known MemberMember

    That's nice to have the valves separated.

    In many canisters, the valves are "ganged" together so that operating one operates the other simultaneously. This is done in some Sun Suns, for example, and integrated with a latch mechanism so that you can close the valves and that releases the tubing assembly from the top of the filter all in one movement. This is very nice for doing filter maintenance because you end up with the tubing remaining primed so that when you start things up again, the system starts up easily and quickly.

    Restricting the flow on the outlet of a centrifugal pump does no damage to the pump. In fact, it lowers the amount of "work" that the pump must do, and that actually reduces the current draw of the pump motor.

    In large pumping systems, automated valves are often used on the outlets of high horsepower centrifugal pumps. When the pump is started, the valve is fully closed. The valve then slowly opens over a period of minutes. This reduces the startup current that the motor will draw which saves a lot of money if the electric utility imposes a surcharge for peak power usage (which most do). It also lessens or eliminates "water hammer", allowing the water in the pipeline to start moving very slowly and gradually ramp up to its full velocity.

    This same valve also slowly closes when the pump is shut off. When you switch off the pump, the pump motor does not immediately shut down. Instead, this valve begins very slowly closing. This gradually slows the movement of the water in the pipeline so that you don't end up with massive "water hammer" which can blow out connections and do amazing damage. Think in terms of stopping a freight train all at once versus gradually braking it to a smooth stop.

    People don't realize the enormous hydraulic forces that come into play if you try to start or stop a pipe full of water suddenly. Where I work, years ago, before I started here, an automatic system shut the filter plant down when a tank got full. Unfortunately, they were doing maintenance on the pond from which we usually draw water, so they had the valving set to feed water directly into the plant from a pipeline fed by large pumps drawing water from the river.

    When the plant shut down, the valves into all of the filters closed automatically, and quickly. The water flowing rapidly in the pipeline (a mile or more long) would have then been required to suddenly all come to a complete stop. This created enough pressure that it separated the pipe right where it comes into the plant, blowing the fittings apart and then flooding the plant basement. It was, from what I hear, quite spectacular! :)

    Anyhow, these special valves, used right on the outlet of very large water pumps, close slowly when you switch a pump off. Only once the valve is completely closed does a limit switch detect that fact, and switch power off to the running pump.

    So on startup and shutdown, all of these pumps operate for quite some time into closed, or tightly throttled valves. This is normal, and does no damage.

    Here's a page for a major manufacturer of this type of "pilot operated" valves:


    Further, prior to us installing variable frequency drives for many of our pumps, we controlled the flow rates by pinching back large valves on the outlets of various pumps. We still have a few 75 horsepower pumps that are throttled that way. Just a manually operated valve right at the outlet of the pump. They run for years this way, and, as I said, they draw less electricity when running this way because, after all, they're doing less work. That seems counter intuitive, but it's the way it works.

    If you have a shop vac, you can prove this to yourself. Simply plug off the outlet momentarily, and see what the motor does. It doesn't slow down, it speeds up! This is because it has less of a load on it when it can't move much or any air. Don't do it for very long, though, because those motors rely on the air they move being sucked over them to cool them.

    On the other hand, if you restrict the flow at the inlet to this type of pump, it creates a vacuum condition and starves the pump. This can cause cavitation which creates noise and can do damage to the pump. In our little aquarium filter pumps, I suspect the damage would be minor, but the noise would be annoying, if nothing else. In larger pumps, the collapsing of the air or steam bubbles created by cavitation can erode hard steel very rapidly, destroying the impellers and even some areas of the stationary parts in short order.

    SnyperTodd addresses this, too, but I'll "pile on". :) The head height doesn't affect any canister filter pump because it's a sealed system and the pump never "sees" any static head. The pump merely circulates the water within a closed system where the "up tube" is balanced exactly by the "down tube".

    Right on, man! :)
    Last edited: Jul 22, 2015
  9. BDpupsWell Known MemberMember

    I know slowing the flow of a canister down doesn't hurt it. But I found a sticky on this forum that says that it does. Just didn't want to rock the boat. I wish the stickies did not get locked. I have found a few with incorrect information in them.

    @SnyperTodd @Jsigmo thanks for explaining it better than I could.

    But when I have too big of a canister on a tank, which I do all the time, I drill the spray bar holes bigger. This works very well for me. And whether I am or not, I feel as if I am getting the full use of the filter this way. If that makes sense :D
    Last edited: Jul 22, 2015
  10. JsigmoWell Known MemberMember

    That makes perfect sense!

    If the problem is that you're getting a very high velocity out of the spray bar, and that's causing problems, then drilling out the holes to lower the velocity out of them makes good sense. Plus, as you point out, it keeps the flow high or even increases it, which does seem better than "wasting" that flow capacity of the filter. :)

    It is unfortunate to have no way to modify a sticky. Then again, I'm sure the moderators could do it in cases where something is incorrect.

    It gets kind of complicated.

    In most filters I've seen, there would be no possible harm from slowing the flow rate down as long as you do it by restricting the outlet side of the system.

    As SnyperTodd mentioned, the only time it could be a problem would be if you slowed the water down so much that it allowed things to overheat. In a filter that has the motor coil outside of the water, even that wouldn't be a concern. And in cases where the motor coil is submerged in the pumped water, you would have to totally stop the flow, or almost totally stop it for it to become an issue because water has such a huge heat capacity that even a tiny trickle will carry an enormous amount of heat away.

    Sometimes, it just takes too much time and space to fully explain something, and there are so many variables to address that people simplify what they write to make the advice "foolproof". Technically, it may not be correct, but at least someone who doesn't understand things fully will avoid problems by following the advice as given, even if it means things won't be optimum.

    In the one tank where I've got a Sun Sun canister, I have the spray bar mounted fairly near the top, yet below the minimum water level by a bit. And I have the holes rotated so that they spray upwards and outwards into the tank. This creates a lot of surface movement, which is what I want, to get good gas transfer, yet it doesn't impose quite so much current in the main part of the water. Of course, it still does create circulation, but in this case, I do want that.

    The cool thing is that we can play with all of this to get the flow pattern and velocities that we want to have.

    The one case where I think you need to observe a particular maximum flow rate through the filter is when you've got a UV sterilizer in place. In that case, you will have an upper flow rate limit in order to assure that the water all receives a high enough dose of the UV radiation to inactivate the organisms in question.

    Of course, as with this thread, there are also obviously other times when you've just got such a small tank that you also need to throttle the output of the filter to keep the water movement to a reasonable level. It always seems like having too much flow in a tank dooms your fishies to living life on a fast-moving treadmill! :)
  11. junebugFishlore LegendMember

    I have a TOM Mini Rapids canister on my 5 gallon right now. I wonder, if I simply slowed the flow down by adding a very small-pore pre-filter sponge to the intake, and possibly changed out the spraybar for something larger, with more holes and therefore wider distribution, if that would work. I was going to just put a small HOB on there, but this might be a good test to see if an 80gph filter can be modified to work on a tank < 5g.

    I also considered taking the canister apart and putting a smaller powerhead on it.
  12. JsigmoWell Known MemberMember

    The problem with adding the sponge pre-filter to the inlet is that by choking off the flow at the inlet, you'll be starving the pump. This may or may not cause problems, but the recommended way to throttle the flow through a pump of this type is to restrict the flow at the outlet of the pump, never the inlet.

    I'd just put a valve in the outlet line and adjust it down to get the flow rate you want. No harm can come from that. :)
  13. junebugFishlore LegendMember

    If I restrict the flow at the outlet, I run the risk of the pump housing basically overflowing. It's happened before - not pretty. The amount of flow reduction to starve the pump would have to be pretty significant... may not be an issue anyway. Those TOM filters have major priming/air suction issues in shallow tanks. Like 5 gallons... lol. Mine started squeaking and shooting bubbles last night when the water level dropped to 3/4" below the tank rim.
  14. JsigmoWell Known MemberMember

    I guess I need to look that filter up. Canisters are usually sealed and cannot overflow. :)
  15. junebugFishlore LegendMember

    The nano ones tend to not be all that great in terms of sealing. I mean this thing sucks air somehow when the water level in the tank gets too low. Nowhere near the intake opening, mind you. But the filter sucks air from somewhere even when everything is closed up. My best guess would be the seal around the compartment housing the powerhead (basically the "lid" of the filter) and the priming hole aren't completely airtight.

    I had another one before that did the same thing. Maybe I'll just look into doing DIY acrylic HOB overflows for my nano tanks. I could turn each one into a refugium and never look back :p LOL.
  16. Frank the Fish guyNew MemberMember

    You might look for a turtle external canister filter. They run a lot smaller and have low flow rates. Same principal as a fish filter.
  17. leftswerveWell Known MemberMember

    There's a possibility that the pressure from restricting the output (or to high of head height) was too much for the seal on the canister housing, especially only less sturdy models.
  18. DolfanFishlore VIPMember

    Tom's makes a pretty good small canister that I have heard of many people using on smaller shrimp/plant tanks. Here is a link from bigalspets.com. It says it is 80gph, so probably more like 60ish when filled up with media and such.

  19. JimWell Known MemberMember

    Totally agree; slowing down either the feed or discharge, restricts the flow of the impeller and will eventually have an effect on the filter motor.

    PS to OP....the Marina HOBs have exceedingly low return flows.
  20. SnyperToddValued MemberMember

    Did you read the previous replies? At least two of us with experience in hydraulics/hydrodynamics/fluid pumps have explained how this is just not true.

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